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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/", | |
}, | |
}, | |
} |
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 relatively simple solution for crawl w/o global variables and channels and with mutex and WaitGroup: