go tour exercises

fibonacci.go

package main

import "fmt"

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

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

io_reader.go

package main

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

type MyReader struct{}

// TODO: Add a Read([]byte) (int, error) method to MyReader.
func (r MyReader) Read(b []byte) (int, error) {
	b[0] = 'A'
	return 1, nil
}

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

map.go

package main

import (
	"strings"

	"golang.org/x/tour/wc"
)

func WordCount(s string) map[string]int {
	m := make(map[string]int)
	for _, w := range strings.Fields(s) {
		//if _, present := m[w]; !present {
		//	m[w] = 0
		//}

		m[w] += 1
	}
	return m
}

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

/*
var m2 = map[int]string{
	1: "a",
	2: "b",
}

// Pointer as key type
var m3 = map[*Vertex]string {
	&Vertex{40.68433, -74.39967,}: "Bell",
	&Vertex{37.42202, -122.08408,}: "Google",
	nil: "nil",
}

// Pointer as value type
var m4 = map[string]*Vertex {
	"Bell Labs": &Vertex{40.68433, -74.39967},
	"Google":    &Vertex{37.42202, -122.08408},
}

// Cannot omit type name `Vertex` if pointer is used as key/value type!
*/

rot13_reader.go

package main

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

type rot13Reader struct {
	r io.Reader
}

func subst(b byte) byte {
	var (
		alpha bool
		start byte
	)
	switch {
	case b >= 'a' && b <= 'z':
		alpha = true
		start = 'a'
	case b >= 'A' && b <= 'Z':
		alpha = true
		start = 'A'
	}
	if alpha {
		return (b+13-start)%26 + start
	}
	return b
}

func (rot13 *rot13Reader) Read(b []byte) (int, error) {
	n, err := rot13.r.Read(b)
	if err == io.EOF {
		return 0, err
	}

	for i, c := range b {
		b[i] = subst(c)
	}
	return n, nil
}

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

slice.go

package main

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

type Selector func(int, int) int

type Renderer func(int, int) [][]uint8

func PicSelector(f Selector) Renderer {
	return func(dx, dy int) [][]uint8 {
		var res [][]uint8

		for y := 0; y < dy; y++ {
			var e []uint8
			for x := 0; x < dx; x++ {
				v := uint8(f(x, y))
				e = append(e, v)
			}
			res = append(res, e)
		}

		return res
	}
}

func main() {
	pic.Show(PicSelector(func(x, y int) int {
		return (x + y) * (x - y)
	}))

}