Go Exercises

equivalent_binary_trees.go

package main

import (
	"code.google.com/p/go-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) {
    defer close(ch) // <- closes the channel when this function returns
    var walk func(t *tree.Tree)
    walk = func(t *tree.Tree) {
        if t == nil {
            return
        }
        walk(t.Left)
        ch <- t.Value
        walk(t.Right)
    }
    walk(t)
}

// Same determines whether the trees
// t1 and t2 contain the same values.
func Same(t1, t2 *tree.Tree) bool {
    ch1, ch2 := make(chan int), make(chan int)

    go Walk(t1, ch1)
    go Walk(t2, ch2)

    for {
        v1,ok1 := <- ch1
        v2,ok2 := <- ch2

        if v1 != v2 || ok1 != ok2 {
            return false
        }

        if !ok1 {
            break
        }
    }

    return true
}

func main() {
	ch := make(chan int)
	go Walk(tree.New(1), ch)
	for i := range ch {
		fmt.Println(i)
	}
	fmt.Println("Should return true:", Same(tree.New(1), tree.New(1)))
	fmt.Println("Should return false:", Same(tree.New(1), tree.New(2)))
}

errors.go

package main

import (
	"fmt"
	"math"
)

type ErrNegativeSqrt float64

func (e ErrNegativeSqrt) Error() string {
	return fmt.Sprintf("cannot Sqrt negative number: %v", float64(e))
}

func Sqrt(x float64) (float64, error) {
	if x < 0 {
		return 0.0, ErrNegativeSqrt(x)
	}
	z := x / 2
	for prev := 0.0; math.Abs(prev-z) > 1e-8; {
		prev = z
		z -= (z*z - x) / (2 * z)
	}
	return z, nil
}

func main() {
	fmt.Println(Sqrt(2))
	fmt.Println(Sqrt(-2))
}

fibonacci.go

package main

import "fmt"

func fibonacci() func() int {
	a, b := 0, 1
	return func() int {
		defer func() { a, b = b, a+b }()
		return a
	}
}

func main() {
	f := fibonacci()
	for i := 0; i < 10; i++ {
		fmt.Println(f())
	}
}

images.go

package main

import (
	"image"
	"image/color"
	"golang.org/x/tour/pic"
)

type Image struct{
	w int
	h int
}

func (i Image) Bounds() image.Rectangle {
	return image.Rect(0, 0, i.w, i.h)
}

func (i Image) ColorModel() color.Model {
	return color.RGBAModel
}

func (i Image) At(x, y int) color.Color {
	r, g, b := uint8(x+y), uint8(x^y), uint8((x+y)/2)
	return color.RGBA{r, g, b, 255}
}

func main() {
	m := Image{100, 100}
	pic.ShowImage(m)
}

loops_and_functions.go

package main

import (
	"fmt"
	"math"
)

func Sqrt(x float64) float64 {
	z := x / 2
	for prev := 0.0; math.Abs(prev-z) > 1e-8; {
		prev = z
		z -= (z*z - x) / (2 * z)
	}
	return z
}

func main() {
	fmt.Println(Sqrt(2))
}

maps.go

package main

import (
	"golang.org/x/tour/wc"
	"strings"
)

func WordCount(s string) map[string]int {
	m := make(map[string]int)
	fields := strings.Fields(s)
	
	for _, v := range fields {
		m[v]++
	}
	
	return m
}

func main() {
	wc.Test(WordCount)
}

readers.go

package main

import "golang.org/x/tour/reader"

type MyReader struct{}

func (r MyReader) Read(b []byte) (int, error) {
	b[0] = 'A'
  	return 1, nil
}

func main() {
	reader.Validate(MyReader{})
}

rot13reader.go

package main

import (
	"io"
	"os"
	"strings"
)

type rot13Reader struct {
	r io.Reader
}

func rot13(b byte) byte {
	var beg byte

	if b >= 'A' && b <= 'Z' {
		beg = 'A'
	} else if b >= 'a' && b <= 'z' {
		beg = 'a'
	} else {
		return b
	}

	return (((b - beg) + 13) % 26) + beg
}

func (r rot13Reader) Read(b []byte) (int, error) {
	size, err := r.r.Read(b)

	for i, v := range b {
		b[i] = rot13(v)
	}

	return size, err
}

func main() {
	s := strings.NewReader("Lbh penpxrq gur pbqr!")
	r := rot13Reader{s}
	io.Copy(os.Stdout, &r)
}

slices.go

package main

import "golang.org/x/tour/pic"

func Pic(dx, dy int) [][]uint8 {
	r := make([][]uint8, dy)
	for i := range r {
		r[i] = make([]uint8, dx)

		for j := range r[i] {
			r[i][j] = image(i, j)
		}
	}
	return r
}

func image(x, y int) uint8 {
	return uint8((y-x)^x-y)
}

func main() {
	pic.Show(Pic)
}

stringers.go

package main

import "fmt"

type IPAddr [4]byte

func (ip IPAddr) String() string {
	return fmt.Sprintf("%d.%d.%d.%d", 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 name, ip := range hosts {
		fmt.Printf("%v: %v\n", name, ip)
	}
}

web_crawler.go

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)
}
type SafeCounter struct {
	v   map[string]bool
	mux sync.Mutex
	wg  sync.WaitGroup
}

var c SafeCounter = SafeCounter{v: make(map[string]bool)}

func (s SafeCounter) checkvisited(url string) bool {
	s.mux.Lock()
	defer s.mux.Unlock()
	_, ok := s.v[url]
	if ok == false {
		s.v[url] = true
		return false
	}
	return true

}

// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher) {
	defer c.wg.Done()
	if depth <= 0 {
		return
	}
	if c.checkvisited(url) {
		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 {
		c.wg.Add(1)
		go Crawl(u, depth-1, fetcher)
	}
	return
}

func main() {
	c.wg.Add(1)
	Crawl("http://golang.org/", 4, fetcher)
	c.wg.Wait()
}

// 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/",
		},
	},
}