package main
import (
 "fmt"
)
func Sqrt(x float64) float64 {
 z := float64(1)
 for i := 0; i <= 10; i++ {
 z = z - (z*z - x) / (2 * z)
 }
 return z
}
func main() {
 fmt.Println(Sqrt(2))
}

package main
import (
 "fmt"
 "math"
)
func Sqrt(x float64) float64 {
 z := float64(1)
 for {
 y := z - (z*z - x) / (2 * z)
 if math.Abs(y - z) < 1e-10 {
 return y
 }
 z = y;
 }
 return z
}
func main() {
 fmt.Println(Sqrt(2))
 fmt.Println(math.Sqrt(2))
}

package main
import (
 "tour/wc"
 "strings"
)
func WordCount(s string) map[string]int {
 ret := make(map[string]int)
 arr := strings.Fields(s)
 for _, val := range arr {
 ret[val]++
 }
 return ret
}
func main() {
 wc.Test(WordCount)
}

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)
 }
 }
 return ret
}
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 {
 sum1 := 0
 sum2 := 1
 return func() int{
 out := sum1 + sum2
 sum1 = sum2
 sum2 = out
 return out
 
 }
}
func main() {
 f := fibonacci()
 for i := 0; i < 10; i++ {
 fmt.Println(f())
 }
}

package main
import (
 "fmt"
 "math/cmplx"
 )
func Cbrt(x complex128) complex128 {
 z := complex128(1)
 for {
 if y := z-(cmplx.Pow(z,3) - x)/(3 * z * z); cmplx.Abs(y - z) < 1e-10 {
 return y
 } else {
 z = y
 }
 }
 return z
}
func main() {
 fmt.Println(Cbrt(2))
}

package main
import (
 "fmt"
 "math"
)
type ErrNegativeSqrt float64
func (e ErrNegativeSqrt) Error() string {
 return "cannot Sqrt negative number:" + fmt.Sprint(float64(e))
}
func Sqrt(f float64) (float64, error) {
 if f < 0 {
 return 0, ErrNegativeSqrt(f)
 }
 
 z := float64(1)
 for {
 y := z - (z*z-f)/(2*z)
 if math.Abs(y-z) < 1e-10 {
 return y, nil
 }
 z = y
 }
 return z, nil
}
func main() {
 fmt.Println(Sqrt(2))
 fmt.Println(Sqrt(-2))
}

package main
import (
 "image"
 "tour/pic"
 "image/color"
)
type Image struct{
 W int
 H int
}
func(self Image) Bounds() image.Rectangle {
 return image.Rect(0, 0, self.W, self.H)
}
func(self Image) ColorModel() color.Model {
 return color.RGBAModel
}
func(self Image) At(x,y int) color.Color {
 return color.RGBA{uint8(x), uint8(y), 255, 255}
}
func main() {
 m := Image{W:100, H:100}
 pic.ShowImage(m)
}

package main
import (
 "io"
 "os"
 "strings"
)
type rot13Reader struct {
 r io.Reader
}
func(self rot13Reader)Read(p []byte) (n int, err error){
 self.r.Read(p)
 leng := len(p)
 for i := 0; i < leng; i++ {
 switch{
 case p[i] >= 'a' && p[i] < 'n':
 fallthrough
 case p[i] >= 'A' && p[i] < 'N':
 p[i] = p[i] + 13
 case p[i] >= 'n' && p[i] <= 'z':
 fallthrough
 case p[i] >= 'N' && p[i] <= 'Z':
 p[i] = p[i] - 13
 }
 }
 return leng, nil
}
func main() {
 s := strings.NewReader(
 "Lbh penpxrq gur pbqr!")
 r := rot13Reader{s}
 io.Copy(os.Stdout, &r)
}

package main
import (
 "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 == nil {
 return
 }
 
 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 func() {
 Walk(t1, ch1)
 ch1 <- 0
 }()
 
 go func() {
 Walk(t2, ch2)
 ch2 <- 0
 }()
 
 for {
 t1 := <-ch1
 t2 := <-ch2
 if t1 == 0 && t2 == 0 {
 return true;
 }
 
 if t1 == t2 {
 continue;
 } else {
 return false;
 }
 }
 return true
}
func main() {
 ch := make(chan int)
 go func() {
 Walk(tree.New(1), ch)
 ch <- 0
 }()
 
 for {
 t := <-ch
 if t == 0 {
 break;
 }
 println(t)
 }
 
 println(Same(tree.New(1), tree.New(2)))
}

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)
}
// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher, out chan string, end chan bool) {
 if depth <= 0 {
 end <- true
 return
 }
 if _, ok := crawled[url]; ok {
 end <- true
 return
 }
 crawledMutex.Lock()
 crawled[url] = true
 crawledMutex.Unlock()
 body, urls, err := fetcher.Fetch(url)
 if err != nil {
 out <- fmt.Sprintln(err)
 end <- true
 return
 }
 out <- fmt.Sprintf("found: %s %q\n", url, body)
 subEnd := make(chan bool)
 for _, u := range urls {
 go Crawl(u, depth-1, fetcher, out, subEnd)
 }
 for i := 0; i < len(urls); i++ {
 <- subEnd
 }
 end <- true
}
var crawled = make(map[string]bool)
var crawledMutex sync.Mutex
func main() {
 out := make(chan string)
 end := make(chan bool)
 go Crawl("http://golang.org/", 4, fetcher, out, end)
 for {
 select {
 case t := <- out:
 fmt.Print(t)
 case <- end:
 return
 }
 }
}
// 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/",
 },
 },
}

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