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tour.golang exercise solutions
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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/", | |
}, | |
}, | |
} |
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...
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my binary tree #67 solution