I am learning Go and the Tour of Go, an interactive tutorial, is a good resource to start with. At the end of each section is a series of exercises for the reader to complete.
Unfortunately, there are no example solutions for those exercises, so its hard to get a hint if you are stuck. Therefore I post my solutions here. I do not think they are the best way to solve the problems in Go (as I said, I am learning too) but code is compiling and it is doing what it should. You are welcome to comment with your solutions and code improvements.
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package main import ( "fmt" "math" ) func Sqrt(x float64) float64 { var z, d float64 = x, 1 for d > 1e-15 { z0 := z z = z-(z*z-x)/(2*z) d = z-z0 if d < 0 { d = -d } } return z } func main() { fmt.Println(Sqrt(2)) fmt.Println(math.Sqrt(2)) } -
package main import ( "strings" "tour/wc" ) func WordCount(s string) map[string]int { m:=make(map[string]int) for _, w:=range strings.Fields(s) { m[w]++ } return m } func main() { wc.Test(WordCount) } -
package main import "tour/pic" func Pic(dx, dy int) [][]uint8 { mat := make([][]uint8, dx) for i := range mat { mat[i] = make([]uint8, dy) for j := range mat[i] { mat[i][j]=uint8(i^j) } } return mat } func main() { pic.Show(Pic) } -
package main import "fmt" // fibonacci is a function that returns // a function that returns an int. func fibonacci() func() int { var a, b, count int = 0, 1, 0 return func() int { switch count { case 0: count++ return a case 1: count++ return b } sum:=a b a=b b=sum return sum } } func main() { f := fibonacci() for i := 0; i < 10; i { fmt.Println(f()) } } Advanced Exercise: Complex cube roots
package main import ( "fmt" "math" "cmath" ) func Cbrt(x complex128) complex128 { var z complex128 = x for i:=0; i 1e-15 { z0 := z z = z-(z*z-f)/(2*z) d = z-z0 if d < 0 { d = -d } } return z, nil } func main() { if value, err := Sqrt(-2.0); err != nil { fmt.Println(err) } else { fmt.Println(value) } }-
package main import ( "image" "tour/pic" ) type Image struct {} func (m *Image) ColorModel() image.ColorModel { return image.RGBAColorModel } func (m *Image) Bounds() image.Rectangle { return image.Rect(0,0,256,256) } func (m *Image) At(x, y int) image.Color { v:=uint8(x^y) return image.RGBAColor{v, v, 255, 255} } func main() { m := &Image{} pic.ShowImage(m) } -
package main import ( "io" "os" "strings" ) type rot13Reader struct { r io.Reader } func rot13(b byte) byte { switch { case 'A' <= b && b <= 'M': b = (b - 'A')+'N' case 'N' <= b && b <= 'Z': b = (b - 'N')+'A' case 'a' <= b && b <= 'm': b = (b - 'a')+'n' case 'n' <= b && b <= 'z': b = (b - 'n')+'a' } return b } func (b *rot13Reader) Read(p []byte) (n int, err os.Error) { n, err = b.r.Read(p) for i:=range(p[:n]) { p[i]=rot13(p[i]) } return } func main() { s := strings.NewReader( "Lbh penpxrq gur pbqr!") r := rot13Reader{s} io.Copy(os.Stdout, &r) } Exercise: Equivalent Binary Trees
package main import ( "fmt" "tour/tree" ) // Walk walks the tree t sending all values // from the tree to the channel ch. func Walk(t *tree.Tree, ch chan int) { if t.Left != nil { Walk(t.Left, ch) } ch<-t.Value if t.Right != nil { 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:=0; i<10; i++ { if <-ch1 != <-ch2 { return false } } return true } func main() { ch := make(chan int) go Walk(tree.New(1), ch) for i:=0; i<10; i++ { fmt.Println(<-ch) } fmt.Println("Equivalent Binary Trees?", Same(tree.New(1), tree.New(1))) fmt.Println("Equivalent Binary Trees?", Same(tree.New(1), tree.New(2))) }-
package main import ( "os" "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 os.Error) } // Crawl uses fetcher to recursively crawl // pages starting with url, to a maximum of depth. func Crawl(url string, depth int, fetcher Fetcher) { type target struct{ urls []string depth int } more := make(chan target) fetchPage := func(url string, depth int) { body, urls, err := fetcher.Fetch(url) if err != nil { fmt.Println(err) } else { fmt.Printf("found: %s %q\n", url, body) } more <- target{urls, depth+1} } go fetchPage(url, 0) visited := map[string]bool{url:true} for counter := 1; counter > 0; { next := <-more counter-- if next.depth > depth { continue } for _, url := range next.urls { if _, seen := visited[url]; seen { continue } visited[url] = true counter++ go fetchPage(url, next.depth) } } } 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, os.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/", }, }, }