11 Solutions of Exercises in GoLangTour

package mainimport (  "fmt"  "math")func Sqrt(x float64) float64 {  z := float64(1)  for i:=1; i<=10; i++ {    fmt.Println(z)    z -= (z * z - x) / (2 * z)  }  return z}func main() {  fmt.Println(Sqrt(2))  fmt.Println(math.Sqrt(2))}

package mainimport "golang.org/x/tour/pic"func Pic(dx, dy int) [][]uint8 {  var result = make([][]uint8, dy)  for x := range result {    result[x] = make([]uint8, dx)    for y:= range result[x] {      result[x][y] = uint8(x*y)    }  }  return result}func main() {  pic.Show(Pic)}

package mainimport ( "golang.org/x/tour/wc" "strings")func WordCount(s string) map[string]int {  result := make(map[string]int)  words := strings.Fields(s)  for _, word := range words {    result[word] += 1  }  return result}func main() {  wc.Test(WordCount)}

package mainimport "fmt"func fibonacci() func() int {  total, nextTotal := 0, 1  return func() int {    result := total    total, nextTotal = nextTotal, nextTotal + result    return result  }}func main() {  f := fibonacci()  for i := 0; i < 10; i++ {    fmt.Println(f())  }}

package mainimport "fmt"type IPAddr [4]bytefunc (ia IPAddr) String() string {  return fmt.Sprintf("%d %d %d %d", ia[0], ia[1], ia[2], ia[3]) }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)  }}

package mainimport ( "fmt" "math")type ErrNegativeSqrt float64func (e ErrNegativeSqrt) Error() string {  return fmt.Sprintf("cannot Sqrt negative number: %d", e)}func Sqrt(x float64) (float64, error) {  if (x < 0) {    return 0, ErrNegativeSqrt(x)   }  z := float64(1)  tolerance := 1e-6  for {    oldz := z    z -= (z * z - x) / (2 * z)    if math.Abs(z-oldz) < tolerance {      break;     }  }  return z, nil}func main() {  fmt.Println(Sqrt(2))  fmt.Println(Sqrt(-2))}

package mainimport "golang.org/x/tour/reader"type MyReader struct{}func (r MyReader) Read(b []byte) (int, error) {  a := 'A'  for i:=0; i < len(b); i++ {    b[i] = a   }  return len(b), nil}// TODO: Add a Read([]byte) (int, error) method to MyReader.func main() {  reader.Validate(MyReader{})}

package mainimport ( "io" "os" "strings")type rot13Reader struct {  r io.Reader}func (rd *rot13Reader) Read(b []byte) (n int, e error) {  n, e = rd.r.Read(b)  for i:=0; i<len(b); i++ {    c := b[i]     if (c >= 'a' && c <= 'm') || (c >= 'A' && c <= 'M')  {      b[i] += 13;        } else if (c >= 'n' && c <= 'z') || (c >= 'N' && c <= 'Z') {      b[i]  -= 13;    }  }   return}func main() {  s := strings.NewReader("Lbh penpxrq gur pbqr!")  r := rot13Reader{s}  io.Copy(os.Stdout, &r)}

package mainimport (  "golang.org/x/tour/pic"  "image"  "image/color")type Image struct{  x int  y int}func (i Image) Bounds() image.Rectangle {  return image.Rect(0, 0, i.x, i.y)}func (i Image) At(x, y int) color.Color {  v := uint8(x*y)  return color.RGBA{v, v, 255, 255}}func (i Image) ColorModel() color.Model {  return color.RGBAModel}func main() {  m := Image{256, 65}  pic.ShowImage(m)}

package mainimport ( "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) {  WalkHelper(t, ch)  close(ch)}func WalkHelper(t *tree.Tree, ch chan int) {  if t == nil {   return   }  WalkHelper(t.Left, ch)  ch <- t.Value  WalkHelper(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 v1 := range ch1 {    v2 := <-ch2    if v1 != v2 {      return false     }  }  return true }func main() {  fmt.Println(Same(tree.New(1), tree.New(1)))   fmt.Println(Same(tree.New(1), tree.New(2))) }

package mainimport (  "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)}var cache = make(Cache)var wg sync.WaitGroupvar mux sync.Mutex// 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 cache.get(url) {    fmt.Printf("xx Skipping: %s\n", url)    return  }  fmt.Printf("** Crawling: %s\n", url)  cache.set(url, true)  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)  for _, u := range urls {    wg.Add(1)    go Crawl(u, depth-1, fetcher)  }  return}func main() {  wg.Add(1)  Crawl("https://golang.org/", 4, fetcher)  wg.Wait()}type Cache map[string]boolfunc (ch Cache) get(key string) bool {  mux.Lock()  defer mux.Unlock()  return cache[key]}func (ch Cache) set(key string, value bool) {  mux.Lock()  defer mux.Unlock()  cache[key] = value}// fakeFetcher is Fetcher that returns canned results.type fakeFetcher map[string]*fakeResulttype 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/",  }, },}