Go Tour Exercise

exercise-equivalent-binary-trees.go

package main

import (
	"fmt"

	"golang.org/x/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) {
	recurseWalk(t, ch)
	close(ch)
}

func recurseWalk(t *tree.Tree, ch chan int) {
	if t.Left != nil {
		recurseWalk(t.Left, ch)
	}
	ch <- t.Value
	if t.Right != nil {
		recurseWalk(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() {
	ch := make(chan int)
	go Walk(tree.New(1), ch)
	for i := 0; i < 10; i++ {
		fmt.Println(<-ch)
	}
	fmt.Println(Same(tree.New(1), tree.New(1)))
	fmt.Println(Same(tree.New(1), tree.New(2)))
}

exercise-errors.go

package main

import (
	"fmt"
)

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, ErrNegativeSqrt(x)
	}
	var v float64
	z := float64(1)
	for float32(v) != float32(z) {
		v = z
		z -= (z*z - x) / (2 * z)
	}
	return z, nil
}

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

exercise-fibonacci-closure.go

package main

import "fmt"

// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
	x, y, z := 0, 0, 1
	return func() int {
		x = y
		y = z
		z = x + y
		return x
	}
}

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

exercise-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 {
	v := uint8((x + y) / 2)
	return color.RGBA{v, v, 255, 255}
}

func main() {
	m := Image{255, 255}
	pic.ShowImage(m)
}

exercise-loops-and-functions.go

package main

import (
	"fmt"
)

func Sqrt(x float64) float64 {
	var v float64
	z := float64(1)
	for float32(v) != float32(z) {
		v = z
		z -= (z*z - x) / (2 * z)
	}
	return z
}

func main() {
	fmt.Println(Sqrt(16))
}

exercise-maps.go

package main

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

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

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

exercise-reader.go

package main

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

type MyReader struct{}

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

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

exercise-rot-reader.go

package main

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

type rot13Reader struct {
	r io.Reader
}

func (rot rot13Reader) Read(b []byte) (int, error) {
	n, err := rot.r.Read(b)
	for i := range b {
		switch {
		case 'A' <= b[i] && 'M' >= b[i]:
			fallthrough
		case 'a' <= b[i] && 'm' >= b[i]:
			b[i] += 13
		case 'N' <= b[i] && 'Z' >= b[i]:
			fallthrough
		case 'n' <= b[i] && 'z' >= b[i]:
			b[i] -= 13
		} 
	}
	return n, err
}

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

exercise-slices.go

package main

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

func Pic(dx, dy int) [][]uint8 {
	data := make([][]uint8, dy)
	for y := 0; y < dy; y++ {
		data[y] = make([]uint8, dx)
		for x := 0; x < dx; x++ {
			data[y][x] = uint8((x + y) / 2)
		}
	}
	return data
}

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

exercise-stringer.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)
	}
}