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/* Exercise: Loops and Functions #43 */ | |
package main | |
import ( | |
"fmt" | |
"math" | |
) | |
func Sqrt(x float64) float64 { | |
z := float64(2.) | |
s := float64(0) | |
for { | |
z = z - (z*z - x)/(2*z) | |
if math.Abs(s-z) < 1e-15 { | |
break | |
} | |
s = z | |
} | |
return s | |
} | |
func main() { | |
fmt.Println(Sqrt(2)) | |
fmt.Println(math.Sqrt(2)) | |
} | |
/******************************************************************************************************/ | |
/* Exercise: Maps #44 */ | |
package main | |
import ( | |
"tour/wc" | |
"strings" | |
) | |
func WordCount(s string) map[string]int { | |
ss := strings.Fields(s) | |
num := len(ss) | |
ret := make(map[string]int) | |
for i := 0; i < num; i++ { | |
(ret[ss[i]])++ | |
} | |
return ret | |
} | |
func main() { | |
wc.Test(WordCount) | |
} | |
/******************************************************************************************************/ | |
/* Exercise: Slices #45 */ | |
package main | |
import "tour/pic" | |
func Pic(dx, dy int) [][]uint8 { | |
ret := make([][]uint8, dy) | |
for i := 0; i < dy; i++ { | |
ret[i] = make([]uint8, dx) | |
for j := 0; j < dx; j++ { | |
ret[i][j] = uint8(i^j+(i+j)/2) | |
} | |
} | |
return ret | |
} | |
func main() { | |
pic.Show(Pic) | |
} | |
/******************************************************************************************************/ | |
/* Exercise: Fibonacci closure #46 */ | |
package main | |
import "fmt" | |
// fibonacci is a function that returns | |
// a function that returns an int. | |
func fibonacci() func() int { | |
var x, y = 0, 1 | |
return func() (z int) { | |
z, x, y = x, y, x+y | |
return | |
} | |
} | |
func main() { | |
f := fibonacci() | |
for i := 0; i < 10; i++ { | |
fmt.Println(f()) | |
} | |
} | |
/******************************************************************************************************/ | |
/* Advanced Exercise: Complex cube roots #47 */ | |
package main | |
import ( | |
"fmt" | |
"math/cmplx" | |
) | |
func Cbrt(x complex128) complex128 { | |
z := complex128(2) | |
s := complex128(0) | |
for { | |
z = z - (cmplx.Pow(z,3) - x)/(3 * (z * z)) | |
if cmplx.Abs(s-z) < 1e-17 { | |
break | |
} | |
s = z | |
} | |
return z | |
} | |
func main() { | |
fmt.Println(Cbrt(2)) | |
} | |
/******************************************************************************************************/ | |
/* Exercise: Errors #57 */ | |
package main | |
import ( | |
"fmt" | |
) | |
type ErrNegativeSqrt float64 | |
func (e ErrNegativeSqrt) Error() string { | |
return fmt.Sprintf("cannot Sqrt negativ number: %g", float64(e)) | |
} | |
func Sqrt(f float64) (float64, error) { | |
if f < 0 { | |
return 0, ErrNegativeSqrt(f) | |
} | |
return 0, nil | |
} | |
func main() { | |
fmt.Println(Sqrt(2)) | |
fmt.Println(Sqrt(-2)) | |
} | |
/******************************************************************************************************/ | |
/* Exercise: Images #58 */ | |
package main | |
import ( | |
"image" | |
"tour/pic" | |
"image/color" | |
) | |
type Image struct{ | |
Width, Height int | |
colr uint8 | |
} | |
func (r *Image) Bounds() image.Rectangle { | |
return image.Rect(0, 0, r.Width, r.Height) | |
} | |
func (r *Image) ColorModel() color.Model { | |
return color.RGBAModel | |
} | |
func (r *Image) At(x, y int) color.Color { | |
return color.RGBA{r.colr+uint8(x), r.colr+uint8(y), 255, 255} | |
} | |
func main() { | |
m := Image{100, 100, 128} | |
pic.ShowImage(&m) | |
} | |
/******************************************************************************************************/ | |
/* Exercise: Rot13 Reader #59: 'You cracked the code!' */ | |
package main | |
import ( | |
"io" | |
"os" | |
"strings" | |
) | |
type rot13Reader struct { | |
r io.Reader | |
} | |
func (rot *rot13Reader) Read(p []byte) (n int, err error) { | |
n,err = rot.r.Read(p) | |
for i := 0; i < len(p); i++ { | |
if (p[i] >= 'A' && p[i] < 'N') || (p[i] >='a' && p[i] < 'n') { | |
p[i] += 13 | |
} else if (p[i] > 'M' && p[i] <= 'Z') || (p[i] > 'm' && p[i] <= 'z'){ | |
p[i] -= 13 | |
} | |
} | |
return | |
} | |
func main() { | |
s := strings.NewReader( | |
"Lbh penpxrq gur pbqr!") | |
r := rot13Reader{s} | |
io.Copy(os.Stdout, &r) | |
} | |
/******************************************************************************************************/ | |
/* Exercise: Equivalent Binary Trees #67 */ | |
package main | |
import ( | |
"tour/tree" | |
"fmt" | |
) | |
// Walk walks the tree t sending all values | |
// from the tree to the channel ch. | |
func Walk(t *tree.Tree, ch chan int) { | |
_walk(t, ch) | |
close(ch) | |
} | |
func _walk(t *tree.Tree, ch chan int) { | |
if t != nil { | |
_walk(t.Left, ch) | |
ch <- t.Value | |
_walk(t.Right, ch) | |
} | |
} | |
// Same determines whether the trees | |
// t1 and t2 contain the same values. | |
func Same(t1, t2 *tree.Tree) bool { | |
ch1 := make(chan int) | |
ch2 := make(chan int) | |
go Walk(t1, ch1) | |
go Walk(t2, ch2) | |
for i := range ch1 { | |
if i != <- ch2 { | |
return false | |
} | |
} | |
return true | |
} | |
func main() { | |
//tree.New(2) | |
ch := make(chan int) | |
go Walk(tree.New(1), ch) | |
for v := range ch { | |
fmt.Print(v) | |
} | |
fmt.Println(Same(tree.New(1), tree.New(1))) | |
fmt.Println(Same(tree.New(1), tree.New(2))) | |
} | |
/******************************************************************************************************/ | |
/* Exercise: Web Crawler #69 */ | |
package main | |
import ( | |
"fmt" | |
) | |
type Fetcher interface { | |
// Fetch returns the body of URL and | |
// a slice of URLs found on that page. | |
Fetch(url string) (body string, urls []string, err error) | |
} | |
var store map[string]bool | |
func Krawl(url string, fetcher Fetcher, Urls chan []string) { | |
body, urls, err := fetcher.Fetch(url) | |
if err != nil { | |
fmt.Println(err) | |
} else { | |
fmt.Printf("found: %s %q\n", url, body) | |
} | |
Urls <- urls | |
} | |
func Crawl(url string, depth int, fetcher Fetcher) { | |
Urls := make(chan []string) | |
go Krawl(url, fetcher, Urls) | |
band := 1 | |
store[url] = true // init for level 0 done | |
for i := 0; i < depth; i++ { | |
for band > 0 { | |
band-- | |
next := <- Urls | |
for _, url := range next { | |
if _, done := store[url] ; !done { | |
store[url] = true | |
band++ | |
go Krawl(url, fetcher, Urls) | |
} | |
} | |
} | |
} | |
return | |
} | |
func main() { | |
store = make(map[string]bool) | |
Crawl("http://golang.org/", 4, fetcher) | |
} | |
// fakeFetcher is Fetcher that returns canned results. | |
type fakeFetcher map[string]*fakeResult | |
type fakeResult struct { | |
body string | |
urls []string | |
} | |
func (f *fakeFetcher) Fetch(url string) (string, []string, error) { | |
if res, ok := (*f)[url]; ok { | |
return res.body, res.urls, nil | |
} | |
return "", nil, fmt.Errorf("not found: %s", url) | |
} | |
// fetcher is a populated fakeFetcher. | |
var fetcher = &fakeFetcher{ | |
"http://golang.org/": &fakeResult{ | |
"The Go Programming Language", | |
[]string{ | |
"http://golang.org/pkg/", | |
"http://golang.org/cmd/", | |
}, | |
}, | |
"http://golang.org/pkg/": &fakeResult{ | |
"Packages", | |
[]string{ | |
"http://golang.org/", | |
"http://golang.org/cmd/", | |
"http://golang.org/pkg/fmt/", | |
"http://golang.org/pkg/os/", | |
}, | |
}, | |
"http://golang.org/pkg/fmt/": &fakeResult{ | |
"Package fmt", | |
[]string{ | |
"http://golang.org/", | |
"http://golang.org/pkg/", | |
}, | |
}, | |
"http://golang.org/pkg/os/": &fakeResult{ | |
"Package os", | |
[]string{ | |
"http://golang.org/", | |
"http://golang.org/pkg/", | |
}, | |
}, | |
} |
I want to share my solution for the image exercise (number 25) with you and everyone who stumbles over this post.
package main
import (
"golang.org/x/tour/pic"
"image/color"
"image"
)
type Image struct{
Rect image.Rectangle
}
func (image Image) ColorModel() color.Model {
return color.RGBAModel
}
func (i Image) Bounds() image.Rectangle {
return i.Rect
}
func (image Image) At(x, y int) color.Color {
return color.RGBA{uint8(x*y), uint8(y+x), 255, 255}
}
func main() {
m := Image{image.Rect(0,0,300,300)}
pic.ShowImage(m)
}
/* Exercise: Web Crawler #69 - https://tour.golang.org/concurrency/10 */
package main
import (
"fmt"
"sync"
)
type Set struct {
v map[string]bool
mux sync.Mutex
}
func (set *Set) Register(key string) {
set.mux.Lock()
defer set.mux.Unlock()
set.v[key] = true
}
func (set *Set) Exists(key string) bool {
set.mux.Lock()
defer set.mux.Unlock()
return set.v[key]
}
type Fetcher interface {
Fetch(url string) (body string, urls []string, err error)
}
func Crawl(url string, depth int, fetcher Fetcher, ch chan string) {
set := Set{v: make(map[string]bool)}
var wg sync.WaitGroup
wg.Add(1)
go crawl(url, depth, fetcher, set, ch, &wg)
wg.Wait()
close(ch)
}
func crawl(url string, depth int, fetcher Fetcher, set Set, ch chan string, wg *sync.WaitGroup) {
defer wg.Done()
if depth <= 0 || set.Exists(url) {
return
}
body, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
return
}
set.Register(url)
ch <- url
fmt.Printf("found: %s %q\n", url, body)
for _, u := range urls {
if set.Exists(u) {
continue
}
wg.Add(1)
go crawl(u, depth-1, fetcher, set, ch, wg)
}
return
}
func main() {
ch := make(chan string)
go Crawl("http://golang.org/", 4, fetcher, ch)
for value := range ch {
fmt.Println(value)
}
}
// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult
type fakeResult struct {
body string
urls []string
}
func (f fakeFetcher) Fetch(url string) (string, []string, error) {
if res, ok := f[url]; ok {
return res.body, res.urls, nil
}
return "", nil, fmt.Errorf("not found: %s", url)
}
// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{
"http://golang.org/": &fakeResult{
"The Go Programming Language",
[]string{
"http://golang.org/pkg/",
"http://golang.org/cmd/",
},
},
"http://golang.org/pkg/": &fakeResult{
"Packages",
[]string{
"http://golang.org/",
"http://golang.org/cmd/",
"http://golang.org/pkg/fmt/",
"http://golang.org/pkg/os/",
},
},
"http://golang.org/pkg/fmt/": &fakeResult{
"Package fmt",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
"http://golang.org/pkg/os/": &fakeResult{
"Package os",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
}
My Solution for stringers does not have any sense, but if condition will be slice of bytes for IPAddr
(dynamic size):
package main
import (
"fmt"
"strings"
"strconv"
)
type IPAddr [4]byte
// TODO: Add a "String() string" method to IPAddr.
func (ipaddr IPAddr) String() string {
var strs []string
for _, v := range ipaddr {
strs = append(
strs, strconv.Itoa(int(v)))
}
return strings.Join(strs, ".")
}
func main() {
hosts := map[string]IPAddr{
"loopback": {127, 0, 0, 1},
"googleDNS": {8, 8, 8, 8},
}
for name, ip := range hosts {
fmt.Printf("%v: %v\n", name, ip)
}
}
/* Exercise: Loops and Functions #43 */
package go_play
import "math"
const (
Delta = 0.01
)
// By dividing by x regardless of the scale of x
// the difference should maintain a constant percentage via its fractional value.
// https://sites.google.com/a/stonybrook.edu/functional-programming-scala/lecture-1-5
func isGoodEnough(guess, x float64) bool {
return math.Abs((guess * guess) - x) / x < Delta // divide by x
}
func iter(zN, x float64) float64 {
zN1 := zN - (zN * zN - x) / (2 * zN)
return zN1
}
func Sqrt(x float64) float64 {
x0 := x
guess := x
for ; isGoodEnough(guess, x); guess = iter(x0, x) {
x0 = guess
}
return guess
}
@zyxar , for #67, even though the test cases the question provided passed, that solution will not pass when ch2
has more elements. It even gets panic when ch2
has fewer elements.
My solution #69 WebCrawler using Mutex
My specific changes are only in provided Crawl function (and of course, the declaration for Cache type)
package main
import (
"fmt"
"sync"
)
type Fetcher interface {
// Fetch returns the body of URL and
// a slice of URLs found on that page.
Fetch(url string) (body string, urls []string, err error)
}
type Cache struct {
uniqueUrl map[string]int
mutx sync.Mutex
}
var myCache = Cache{uniqueUrl:make(map[string]int)}
var wg sync.WaitGroup // required to let all launched goroutines finish before main() exits
// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher) {
defer wg.Done()
if depth <= 0 {
return
}
_, visited := myCache.uniqueUrl[url]
if visited {
return
}
myCache.mutx.Lock()
myCache.uniqueUrl[url] = 1
myCache.mutx.Unlock()
body, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("found: %s %q\n", url, body)
for _, u := range urls {
wg.Add(1)
go Crawl(u, depth-1, fetcher)
}
return
}
func main() {
wg.Add(1)
Crawl("http://golang.org/", 4, fetcher)
wg.Wait()
}
// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult
type fakeResult struct {
body string
urls []string
}
func (f fakeFetcher) Fetch(url string) (string, []string, error) {
if res, ok := f[url]; ok {
return res.body, res.urls, nil
}
return "", nil, fmt.Errorf("***not found: %s", url)
}
// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{
"http://golang.org/": &fakeResult{
"The Go Programming Language",
[]string{
"http://golang.org/pkg/",
"http://golang.org/cmd/",
},
},
"http://golang.org/pkg/": &fakeResult{
"Packages",
[]string{
"http://golang.org/",
"http://golang.org/cmd/",
"http://golang.org/pkg/fmt/",
"http://golang.org/pkg/os/",
},
},
"http://golang.org/pkg/fmt/": &fakeResult{
"Package fmt",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
"http://golang.org/pkg/os/": &fakeResult{
"Package os",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
}
My crawler:
package main
import (
"fmt"
"sync"
"time"
)
type Fetcher interface {
// Fetch returns the body of URL and
// a slice of URLs found on that page.
Fetch(url string) (body string, urls []string, err error)
}
type Crawler struct {
baseUrl string
depth int
fetcher *Fetcher
cache map[string] bool
active int
mux sync.Mutex
}
func NewCrawler(baseUrl string, depth int, fetcher *Fetcher) *Crawler {
return &Crawler{
baseUrl: baseUrl,
depth: depth,
cache: make(map[string] bool),
fetcher: fetcher,
}
}
func (c *Crawler) RegisterWorker() {
c.mux.Lock()
c.active++
c.mux.Unlock()
}
func (c *Crawler) DeregisterWorkerAndMaybeCloseChannel(ch chan<- string) {
c.mux.Lock()
c.active--
if c.active <= 0 {
close(ch)
}
c.mux.Unlock()
}
func (c *Crawler) CheckUrl(url string) bool {
c.mux.Lock()
defer c.mux.Unlock()
if _, ok := c.cache[url]; ok {
return false
}
c.cache[url] = true
return true
}
func (c *Crawler) Work(url string, currentDepth int, urlsChannel chan<- string) {
if currentDepth <= 0 || !c.CheckUrl(url) {
c.DeregisterWorkerAndMaybeCloseChannel(urlsChannel)
return
}
_, urls, err := (*c.fetcher).Fetch(url)
if err != nil {
fmt.Println(err)
c.DeregisterWorkerAndMaybeCloseChannel(urlsChannel)
return
}
urlsChannel <- url
for _, subUrl := range urls {
c.RegisterWorker()
go c.Work(subUrl, currentDepth - 1, urlsChannel)
}
c.DeregisterWorkerAndMaybeCloseChannel(urlsChannel)
}
func (c *Crawler) Crawl(urlsChannel chan<- string) {
c.RegisterWorker()
go c.Work(c.baseUrl, c.depth, urlsChannel)
}
// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher) {
urls := make(chan string)
crawler := NewCrawler(url, depth, &fetcher)
crawler.Crawl(urls)
for u := range urls {
fmt.Println("Got url:", u)
}
}
func main() {
Crawl("http://golang.org/", 4, fetcher)
}
// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult
type fakeResult struct {
body string
urls []string
}
func (f fakeFetcher) Fetch(url string) (string, []string, error) {
time.Sleep(200 * time.Millisecond)
if res, ok := f[url]; ok {
return res.body, res.urls, nil
}
return "", nil, fmt.Errorf("not found: %s", url)
}
// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{
"http://golang.org/": &fakeResult{
"The Go Programming Language",
[]string{
"http://golang.org/pkg/",
"http://golang.org/cmd/",
},
},
"http://golang.org/pkg/": &fakeResult{
"Packages",
[]string{
"http://golang.org/",
"http://golang.org/cmd/",
"http://golang.org/pkg/fmt/",
"http://golang.org/pkg/os/",
},
},
"http://golang.org/pkg/fmt/": &fakeResult{
"Package fmt",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
"http://golang.org/pkg/os/": &fakeResult{
"Package os",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
}
My solution #69 WebCrawler using Mutex
package main
import (
"fmt"
"sync"
"time"
)
type urlCache struct{
m map[string]bool
mux sync.Mutex
}
func (uc *urlCache) Add(url string){
uc.mux.Lock()
uc.m[url] = true
uc.mux.Unlock()
}
func (uc *urlCache) Value(url string) bool{
uc.mux.Lock()
defer uc.mux.Unlock()
return uc.m[url]
}
type Fetcher interface {
// Fetch returns the body of URL and
// a slice of URLs found on that page.
Fetch(url string) (body string, urls []string, err error)
}
// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher,uc *urlCache) {
// TODO: Fetch URLs in parallel.
// TODO: Don't fetch the same URL twice.
// This implementation doesn't do either:
if depth <= 0 {
return
}
if uc.Value(url) {
//fmt.Println(url," is fetched")
return
}
body, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
return
}
uc.Add(url)
fmt.Printf("found: %s %q\n", url, body)
for _, u := range urls {
//fmt.Println(u)
go Crawl(u, depth-1, fetcher,uc)
}
return
}
func main() {
uc := urlCache{m:make(map[string]bool)}
go Crawl("http://golang.org/", 4, fetcher,&uc)
time.Sleep(time.Second)
}
// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult
type fakeResult struct {
body string
urls []string
}
func (f fakeFetcher) Fetch(url string) (string, []string, error) {
if res, ok := f[url]; ok {
return res.body, res.urls, nil
}
return "", nil, fmt.Errorf("not found: %s", url)
}
// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{
"http://golang.org/": &fakeResult{
"The Go Programming Language",
[]string{
"http://golang.org/pkg/",
"http://golang.org/cmd/",
},
},
"http://golang.org/pkg/": &fakeResult{
"Packages",
[]string{
"http://golang.org/",
"http://golang.org/cmd/",
"http://golang.org/pkg/fmt/",
"http://golang.org/pkg/os/",
},
},
"http://golang.org/pkg/fmt/": &fakeResult{
"Package fmt",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
"http://golang.org/pkg/os/": &fakeResult{
"Package os",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
}
I apologize that I didn´t check all the above comments.
There are too many.
There are two problems for the Web Crawler:
- mutual exclusion of the map
- termination of the go routines (Crawl): It is necessary to check if the all the go routines terminated.
The solution for the mutual exclusion is straightforward. I used sync.Mutex
For the termination, I used the Dijkstra & Scholten idea. It is simple and it is detailed in "Termination Detection for Diffusing Computations", Information Processing Letters, Vol. 11, No. 1, Aug. 1980.
package main
import (
"fmt"
"sync"
)
// SafeMap is safe map of URL to use concurrently.
type SafeMap struct {
v map[string]int
mux sync.Mutex
}
func (c *SafeMap) Ins(key string) {
c.mux.Lock()
c.v[key]++
c.mux.Unlock()
}
func (c *SafeMap) HasValue(key string) bool {
c.mux.Lock()
defer c.mux.Unlock()
_, ok:= c.v[key]
return ok
}
type Fetcher interface {
// Fetch returns the body of URL and
// a slice of URLs found on that page.
Fetch(url string) (body string, urls []string, err error)
}
// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher, ch chan int) {
// TODO: Fetch URLs in parallel.
// TODO: Don't fetch the same URL twice.
// This implementation doesn't do either:
defer func () {ch <-1} ()
if depth <= 0 {
return
}
ok := c.HasValue(url)
if ok {
//fmt.Println("URL alread in the map",url)
return
} else {
c.Ins(url)
}
body, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("found: %s %q\n", url, body)
nUrls := len(urls)
chs := make(chan int)
for _, u := range urls {
go Crawl(u, depth-1, fetcher, chs)
}
for i:=0; i<nUrls; i++ {<-chs}
return
}
var c=SafeMap{v:make(map[string]int)}
func main() {
ch := make(chan int)
go Crawl("http://golang.org/", 4, fetcher, ch)
fmt.Println("Processed ",<-ch)
}
// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult
type fakeResult struct {
body string
urls []string
}
func (f fakeFetcher) Fetch(url string) (string, []string, error) {
if res, ok := f[url]; ok {
return res.body, res.urls, nil
}
return "", nil, fmt.Errorf("not found: %s", url)
}
// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{
"http://golang.org/": &fakeResult{
"The Go Programming Language",
[]string{
"http://golang.org/pkg/",
"http://golang.org/cmd/",
},
},
"http://golang.org/pkg/": &fakeResult{
"Packages",
[]string{
"http://golang.org/",
"http://golang.org/cmd/",
"http://golang.org/pkg/fmt/",
"http://golang.org/pkg/os/",
},
},
"http://golang.org/pkg/fmt/": &fakeResult{
"Package fmt",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
"http://golang.org/pkg/os/": &fakeResult{
"Package os",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
}
My solution using sync.Mutex
package main
import (
"fmt"
"sync"
)
type Fetcher interface {
// Fetch returns the body of URL and
// a slice of URLs found on that page.
Fetch(url string) (body string, urls []string, err error)
}
func crawl(url string, fetcher Fetcher, Urls chan []string) {
body, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
} else {
fmt.Printf("found: %s %q\n", url, body)
}
Urls <- urls
}
// SafeUrls is safe to use concurrently.
type SafeUrls struct {
v map[string]bool
mux sync.Mutex
}
var Urls chan []string = make(chan []string)
// Set url visited for the given key.
func (c *SafeUrls) Add(key string) {
c.mux.Lock()
// Lock so only one goroutine at a time can access the map c.v.
c.v[key] = true
c.mux.Unlock()
}
// Value returns the current value of the urls for the given key.
func (c *SafeUrls) Value(key string) bool {
c.mux.Lock()
// Lock so only one goroutine at a time can access the map c.v.
defer c.mux.Unlock()
return c.v[key]
}
// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher) {
if depth <= 0 {
return
}
go crawl(url, fetcher, Urls)
urls := <- Urls
for _, u := range urls {
Crawl(u, depth-1, fetcher)
}
return
}
func main() {
Crawl("http://golang.org/", 4, fetcher)
}
// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult
type fakeResult struct {
body string
urls []string
}
func (f fakeFetcher) Fetch(url string) (string, []string, error) {
if res, ok := f[url]; ok {
return res.body, res.urls, nil
}
return "", nil, fmt.Errorf("not found: %s", url)
}
// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{
"http://golang.org/": &fakeResult{
"The Go Programming Language",
[]string{
"http://golang.org/pkg/",
"http://golang.org/cmd/",
},
},
"http://golang.org/pkg/": &fakeResult{
"Packages",
[]string{
"http://golang.org/",
"http://golang.org/cmd/",
"http://golang.org/pkg/fmt/",
"http://golang.org/pkg/os/",
},
},
"http://golang.org/pkg/fmt/": &fakeResult{
"Package fmt",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
"http://golang.org/pkg/os/": &fakeResult{
"Package os",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
}
Here is my solution to the crawler. It uses a mutex within the url cache and a wait group in order to terminate once all go routines have finished. I'm not sure whether this is idiomatic or not (especially with the UrlCache
, and Crawler
structs/methods), if anyone has any feedback I would appreciate it.
package main
import (
"fmt"
"sync"
)
type Fetcher interface {
Fetch(url string) (body string, urls []string, err error)
}
type UrlCache struct {
urls map[string]bool
mux sync.Mutex
}
func (cache *UrlCache) Add(url string) {
cache.mux.Lock()
cache.urls[url] = true
cache.mux.Unlock()
}
func (cache *UrlCache) Contains(url string) bool {
cache.mux.Lock()
defer cache.mux.Unlock()
return cache.urls[url]
}
type Crawler struct {
urlCache UrlCache
fetcher Fetcher
waitGroup sync.WaitGroup
}
func (crawler *Crawler) Crawl(url string, depth int) {
defer crawler.waitGroup.Done()
if depth <= 0 {
return
}
if crawler.urlCache.Contains(url) {
return
}
_, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Errorf("crawl: error when fetching url %s %v\n", url, err)
return
}
fmt.Printf("visited %s - %d urls found\n", url, len(urls))
crawler.urlCache.Add(url)
for _, u := range urls {
crawler.waitGroup.Add(1)
go crawler.Crawl(u, depth-1)
}
}
func main() {
waitGroup := sync.WaitGroup{}
waitGroup.Add(1)
crawler := Crawler{
urlCache: UrlCache{urls: make(map[string]bool)},
fetcher: fetcher,
waitGroup: waitGroup,
}
go crawler.Crawl("http://golang.org/", 4)
crawler.waitGroup.Wait()
}
// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult
type fakeResult struct {
body string
urls []string
}
func (f fakeFetcher) Fetch(url string) (string, []string, error) {
if res, ok := f[url]; ok {
return res.body, res.urls, nil
}
return "", nil, fmt.Errorf("not found: %s", url)
}
// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{
"http://golang.org/": &fakeResult{
"The Go Programming Language",
[]string{
"http://golang.org/pkg/",
"http://golang.org/cmd/",
},
},
"http://golang.org/pkg/": &fakeResult{
"Packages",
[]string{
"http://golang.org/",
"http://golang.org/cmd/",
"http://golang.org/pkg/fmt/",
"http://golang.org/pkg/os/",
},
},
"http://golang.org/pkg/fmt/": &fakeResult{
"Package fmt",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
"http://golang.org/pkg/os/": &fakeResult{
"Package os",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
}
At line 61 the code :
ret[i] = make([]uint8, dx)
Can you tell me what is the reasoning behind using dx
as length of slice? It doesnt say the length is dx
but slice is of dx
elements. Kinda confused :/
if we know that trees have 10 nodes, then this variant has a chance of life)):
package main
import (
"golang.org/x/tour/tree"
"fmt"
"sort"
)
// Walk walks the tree t sending all values
// from the tree to the channel ch.
//var cnt1 chan int
func Walk(t *tree.Tree, ch chan int) {
if t != nil {
ch <- t.Value
count:=<-ch
if count == 10 {
close(ch)
return}
Walk(t.Right, ch)
Walk(t.Left, ch)
}
}
// Same determines whether the trees
// t1 and t2 contain the same values.
func Same(t1, t2 *tree.Tree) bool {
ch1 := make(chan int)
go Walk(t1, ch1)
ch2 := make(chan int)
go Walk(t2, ch2)
var n1 [10]int
var n2 [10]int
i1,i2 := 0, 0
for i:=range ch1 {
n1[i1] = i
i1++
ch1<-i1
}
for i:=range ch2 {
n2[i2] = i
i2++
ch2<-i2
}
sort.Ints(n1[:])
sort.Ints(n2[:])
if n1 == n2 {
return true
} else {return false}
}
func main() {
fmt.Println(Same(tree.New(1), tree.New(1)))
fmt.Println(Same(tree.New(1), tree.New(2)))
}
for Crawler, I only used knowledge from previous lessons, such as a SafeCouter (without sync.WaitGroup)
package main
import (
"fmt"
"sync"
"time"
)
type Fetcher interface {
// Fetch returns the body of URL and
// a slice of URLs found on that page.
Fetch(url string) (body string, urls []string, err error)
}
type SafeHashset struct {
mux sync.Mutex
h map[string]bool
}
func (counter *SafeCounter) Inc(inc int) {
counter.mux.Lock()
defer counter.mux.Unlock()
counter.c = counter.c + inc
}
type SafeCounter struct {
mux sync.Mutex
c int
}
func (counter *SafeCounter) Value() int {
counter.mux.Lock()
defer counter.mux.Unlock()
return counter.c
}
func (hashset *SafeHashset) Add(url string) bool {
hashset.mux.Lock()
defer hashset.mux.Unlock()
if _, ok := hashset.h[url]; !ok {
hashset.h[url] = true
return true
} else {
return false
}
}
//var ch chan struct{} = make(chan struct {})
// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
var hashset = SafeHashset{h: make(map[string]bool)}
var count =SafeCounter{}
func Crawl(url string, depth int, fetcher Fetcher) {
defer count.Inc(-1)
// TODO: Fetch URLs in parallel.
// TODO: Don't fetch the same URL twice.
// This implementation doesn't do either:
if depth <= 0 {
return
}
if hashset.Add(url) {
body, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("found: %s %q\n", url, body)
for _, u := range urls {
count.Inc(1)
go Crawl(u, depth-1, fetcher)
//defer <-ch
}
}
return
}
func main() {
count.Inc(1)
Crawl("http://golang.org/", 4, fetcher)
for {
if count.Value() == 0 {
break
}
time.Sleep(time.Second)
}
}
// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult
type fakeResult struct {
body string
urls []string
}
func (f fakeFetcher) Fetch(url string) (string, []string, error) {
if res, ok := f[url]; ok {
return res.body, res.urls, nil
}
return "", nil, fmt.Errorf("not found: %s", url)
}
// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{
"http://golang.org/": &fakeResult{
"The Go Programming Language",
[]string{
"http://golang.org/pkg/",
"http://golang.org/cmd/",
},
},
"http://golang.org/pkg/": &fakeResult{
"Packages",
[]string{
"http://golang.org/",
"http://golang.org/cmd/",
"http://golang.org/pkg/fmt/",
"http://golang.org/pkg/os/",
},
},
"http://golang.org/pkg/fmt/": &fakeResult{
"Package fmt",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
"http://golang.org/pkg/os/": &fakeResult{
"Package os",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
}
my binary tree #67 solution
package main
import (
"golang.org/x/tour/tree"
"fmt"
)
// Walk walks the tree t sending all values
// from the tree to the channel ch.
func Walk(t *tree.Tree, ch chan int, layer int) {
if t == nil {
return
}
Walk(t.Left, ch, layer + 1)
ch <- t.Value
Walk(t.Right, ch, layer + 1)
if layer == 0 {
close(ch)
}
}
// Same determines whether the trees
// t1 and t2 contain the same values.
func Same(t1, t2 *tree.Tree) bool {
ch1 := make(chan int, 10)
ch2 := make(chan int, 10)
go Walk(t1, ch1, 0)
go Walk(t2, ch2, 0)
for {
n1, ok1 := <- ch1
n2, ok2 := <- ch2
if n1 != n2 || ok1 != ok2 {
return false
} else if ok1 == ok2 && ok1 == false {
return true
}
}
}
func main() {
fmt.Println(Same(tree.New(1), tree.New(2)));
fmt.Println(Same(tree.New(1), tree.New(1)));
}
IP Address Solution:
package tour
import "fmt"
type IPAddr [4]byte
func (ipAddr IPAddr) String() string {
return fmt.Sprintf("%d.%d.%d.%d", ipAddr[0], ipAddr[1], ipAddr[2], ipAddr[3])
}
func IPAddress() {
hosts := map[string]IPAddr{
"loopback": {127, 0, 0, 1},
"googleDNS": {8, 8, 8, 8},
}
for name, ip := range hosts {
fmt.Printf("%v: %v\n", name, ip)
}
}
Reader Solution:
package tour
import (
"fmt"
)
type MyReader struct{}
func (r MyReader) Read(b []byte) (int, error) {
bufferLength := len(b)
if bufferLength <= 0 {
return 0, fmt.Errorf("buffer length must be greater than 0")
}
buffer := make([]byte, bufferLength)
for k := range buffer {
buffer[k] = uint8('A')
}
n := copy(b, buffer)
return n, nil
}
rot13Reader Solution:
❓ this solution saves an extra loop by returning io.EOF
as early as possible.
package tour
import (
"io"
"os"
"strings"
)
type rot13Reader struct {
r io.Reader
}
func (r rot13Reader) Read(b []byte) (int, error) {
n, err := r.r.Read(b)
// short circuit: EOF
if err == io.EOF {
return 0, io.EOF
}
for k, v := range b {
b[k] = rot13(v)
}
return n, err
}
func Rot13ReaderMain() {
s := strings.NewReader("Lbh penpxrq gur pbqr!")
r := rot13Reader{s}
io.Copy(os.Stdout, &r)
}
func rot13(b byte) byte {
if b >= 'A' && b <= 'Z' {
b = 'A' + (b-'A'+13)%26
} else if b >= 'a' && b <= 'z' {
b = 'a' + (b-'a'+13)%26
}
return b
}
Images exercise solution:
package tour
import (
"image"
"image/color"
)
type Image struct {
Width int
Height int
}
func (i Image) ColorModel() color.Model {
return color.RGBAModel
}
func (i Image) Bounds() image.Rectangle {
return image.Rect(0, 0, i.Width, i.Height)
}
func (i Image) At(x, y int) color.Color {
r := uint8(x + y)
g := uint8(x ^ y)
b := uint8(x * y)
//fmt.Println("R:", r, "G:", g, "B:", b)
return color.RGBA{r, g, b, 255}
}
This is my solution to the Exercise "Stringers":
package main
import "fmt"
type IPAddr [4]byte
// TODO: Add a "String() string" method to IPAddr.
// What I did was I returned the call to Sprintf (in the fmt package) and formatted each of the four byte values in the array
// of bytes, separated with dots:
func (ip IPAddr) String() string{
// The 'Sprintf' function formats according to a format specifier and returns the resulting string.
// In other words: you first return the resulting string of the function 'Sprintf' and then
// this method (String()) returns the previously returned string by 'Sprintf':
return fmt.Sprintf("%v.%v.%v.%v",ip[0],ip[1],ip[2],ip[3])
}
func main() {
hosts := map[string]IPAddr{
"loopback": {127, 0, 0, 1},
"googleDNS": {8, 8, 8, 8},
}
for nombre, ip := range hosts {
fmt.Printf("%v: %v\n", nombre, ip)
}
}
I hope it helps!
Excuse me:
In the rot13Reader exercise, how is Read(p []byte) called? I'm a bit confused, since I don't see it being invoked in main()...
package main
import (
"io"
"os"
"strings"
)
type rot13Reader struct {
r io.Reader
}
func (rot *rot13Reader) Read(p []byte) (n int, err error) {
n,err = rot.r.Read(p)
for i := 0; i < len(p); i++ {
if (p[i] >= 'A' && p[i] < 'N') || (p[i] >='a' && p[i] < 'n') {
p[i] += 13
} else if (p[i] > 'M' && p[i] <= 'Z') || (p[i] > 'm' && p[i] <= 'z'){
p[i] -= 13
}
}
return
}
func main() {
s := strings.NewReader(
"Lbh penpxrq gur pbqr!")
r := rot13Reader{s}
io.Copy(os.Stdout, &r)
}
MIT Phd crawl solution
package main
import (
"fmt"
"sync"
)
type Cache struct {
m sync.Mutex
v map[string]uint
}
func (s *Cache) Exist(key string) bool {
s.m.Lock()
defer s.m.Unlock()
if _, ok := s.v[key]; ok {
s.v[key]++
return true
} else {
s.v[key] = 1
return false
}
}
func (s *Cache) String() string {
s.m.Lock()
defer s.m.Unlock()
var sb string
for k, v := range s.v {
sb += fmt.Sprintf("key: %s => value: %q", k, v)
}
return fmt.Sprintln(sb)
}
type Fetcher interface {
Fetch(url string) (body string, urls []string, err error)
}
//
// Serial crawler
//
func SerialCrawl(url string, depth int, fetcher Fetcher, cache *Cache) {
if cache.Exist(url) {
return
}
//fmt.Printf("cached values %q\n", cache)
fmt.Println("depth ", depth)
if depth <= 0 {
return
}
body, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("Found: %s %q\n", url, body)
//fmt.Printf("fetch children %q\n", urls)
for _, u := range urls {
//fmt.Printf("recursive crawl url %s\n", u)
SerialCrawl(u, depth-1, fetcher, cache)
}
}
//
// Concurrent crawler with shared state and Mutex
//
func ConcurrentMutex(url string, depth int, fetcher Fetcher, cache *Cache) {
if cache.Exist(url) {
return
}
//fmt.Printf("cached values %q\n", cache)
if depth <= 0 {
return
}
body, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("Found: %s %q\n", url, body)
//fmt.Printf("fetch children %q\n", urls)
var done sync.WaitGroup
for _, u := range urls {
done.Add(1)
//fmt.Printf("recursive crawl url %s\n", u)
u2 := u
go func() {
defer done.Done()
ConcurrentMutex(u2, depth-1, fetcher, cache)
}()
//go func(u string) {
// defer done.Done()
// ConcurrentMutex(u, depth -1,fetcher, cache)
//}(u)
}
done.Wait()
}
//
// Concurrent crawler with channels
//
func worker(url string, depth uint, ch chan []string, fetcher Fetcher, cache *Cache) {
//fmt.Printf("working on url %s depth %d\n", url, depth)
body, urls, err := fetcher.Fetch(url)
if err != nil {
ch <- []string{}
} else {
fmt.Printf("Found: %s %q\n", url, body)
ch <- urls
}
}
func master(url string, ch chan []string, depth uint, fetcher Fetcher, cache *Cache) {
n := 1
copyDepth := depth
for urls := range ch {
// fmt.Printf("dep :%s\n", fmt.Sprintf("%q", copyDepth))
if copyDepth == 0 {
break
}
for _, url := range urls {
if !cache.Exist(url) {
n += 1
go worker(url, depth, ch, fetcher, cache)
}
}
depth--
n -= 1
if n == 0 {
break
}
}
}
func ConcurrentChan(url string, depth uint, fetcher Fetcher, cache *Cache) {
ch := make(chan []string)
go func() {
ch <- []string{url}
}()
master(url, ch, depth, fetcher, cache)
}
func main() {
cache := Cache{v: make(map[string]uint)}
SerialCrawl("https://golang.org/", 4, fetcher, &cache)
ConcurrentMutex("https://golang.org/", 4, fetcher, &cache)
ConcurrentChan("https://golang.org/", 4, fetcher, &cache)
fmt.Printf("\nCached urls %q\n", cache.v)
}
type fakeFetcher map[string]*fakeResult // to avoid copy value
type fakeResult struct {
body string
urls []string
}
func (f fakeFetcher) Fetch(url string) (string, []string, error) {
if res, ok := f[url]; ok {
return res.body, res.urls, nil
}
return "", nil, fmt.Errorf("not found: %s", url)
}
var fetcher = fakeFetcher{
"https://golang.org/": &fakeResult{
"The Go Programming Language",
[]string{
"https://golang.org/pkg/",
"https://golang.org/cmd/",
},
},
"https://golang.org/pkg/": &fakeResult{
"Packages",
[]string{
"https://golang.org/",
"https://golang.org/cmd/",
"https://golang.org/pkg/fmt/",
"https://golang.org/pkg/os/",
},
},
"https://golang.org/pkg/fmt/": &fakeResult{
"Package fmt",
[]string{
"https://golang.org/",
"https://golang.org/pkg/",
},
},
"https://golang.org/pkg/os/": &fakeResult{
"Package os",
[]string{
"https://golang.org/",
"https://golang.org/pkg/",
},
},
}
My relatively simple solution for crawl w/o global variables and channels and with mutex and WaitGroup:
package main
import (
"fmt"
"sync"
)
type UrlCache struct {
urls map[string]bool
mu sync.Mutex
}
func (uc *UrlCache) Add(url string) {
uc.mu.Lock()
uc.urls[url] = true
uc.mu.Unlock()
}
func (uc *UrlCache) Get(url string) bool {
uc.mu.Lock()
defer uc.mu.Unlock()
return uc.urls[url]
}
type Fetcher interface {
// Fetch returns the body of URL and
// a slice of URLs found on that page.
Fetch(url string) (body string, urls []string, err error)
}
// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher) {
var wg sync.WaitGroup
cache := UrlCache{urls: make(map[string]bool)}
wg.Add(1)
go crawl(url, depth, fetcher, &cache, &wg)
wg.Wait()
}
func crawl(url string, depth int, fetcher Fetcher, cache *UrlCache, wg *sync.WaitGroup) {
defer wg.Done()
if depth <= 0 || cache.Get(url) {
return
}
cache.Add(url)
body, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("found: %s %q\n", url, body)
for _, u := range urls {
wg.Add(1)
go crawl(u, depth-1, fetcher, cache, wg)
}
}
func main() {
Crawl("https://golang.org/", 4, fetcher)
}
// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult
type fakeResult struct {
body string
urls []string
}
func (f fakeFetcher) Fetch(url string) (string, []string, error) {
if res, ok := f[url]; ok {
return res.body, res.urls, nil
}
return "", nil, fmt.Errorf("not found: %s", url)
}
// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{
"https://golang.org/": &fakeResult{
"The Go Programming Language",
[]string{
"https://golang.org/pkg/",
"https://golang.org/cmd/",
},
},
"https://golang.org/pkg/": &fakeResult{
"Packages",
[]string{
"https://golang.org/",
"https://golang.org/cmd/",
"https://golang.org/pkg/fmt/",
"https://golang.org/pkg/os/",
},
},
"https://golang.org/pkg/fmt/": &fakeResult{
"Package fmt",
[]string{
"https://golang.org/",
"https://golang.org/pkg/",
},
},
"https://golang.org/pkg/os/": &fakeResult{
"Package os",
[]string{
"https://golang.org/",
"https://golang.org/pkg/",
},
},
}
Reader Solution:
package tour import ( "fmt" ) type MyReader struct{} func (r MyReader) Read(b []byte) (int, error) { bufferLength := len(b) if bufferLength <= 0 { return 0, fmt.Errorf("buffer length must be greater than 0") } buffer := make([]byte, bufferLength) for k := range buffer { buffer[k] = uint8('A') } n := copy(b, buffer) return n, nil }
Is there a reason why you just don't set the 'A' directly in b? Why creating an internal slice and then copying to b? Just curious...
The ro13 solution assumes the lower reader gives the requested number of bytes. This is not necessarily the case so:
for i, b := range p
should be
for i:=0 ; i < n ; i++