Solutions for tour.golang exercises

exercise_45.go

package main

import (
	"fmt"
	"math"
)

func Sqrt(x float64) float64 {
	z, d := 1.0, 1.0
	for d > 1e-4 { //more precise than 1e-4 fails online
		zz := z
		z = z-(z*z-x)/2*z
		d = math.Abs(z-zz)
	}
	return z
}

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

exercise_46.go

package main


import (
	"tour/wc"
	"strings"
)

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

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

exercise_47.go

package main


import "tour/pic"

func Pic(dx, dy int) [][]uint8 {
	slices := make([][]uint8, dy)
	for i := 0; i < dy; i++ {
		slices[i] = make([]uint8, dx)
		for j := 0; j < dx; j++ {
			slices[i][j] = uint8(i^j)
		}	
	}
	return slices
}

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

exercise_48.go

package main

import "fmt"

// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
	fib1, fib2 := 0,1
	return func() int {
		next := fib1
		fib1 = fib1+fib2
		fib2 = next
		return fib1
	}
}

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

exercise_49.go

package main

import (
	"fmt"
	"math/cmplx"
)

func Cbrt(x complex128) complex128 {
	z := complex128(1.0)
	d := 1.0
	for d > 1e-17 {
		zz := z
		z = z-(cmplx.Pow(z, 3)-x)/(3*cmplx.Pow(z, 2))
		d = cmplx.Abs(z-zz)
	}
	return z
}

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

Exercise_58_HTTP_Handlers.go

package main

import (
	"net/http"
	"fmt"
)

type String string

type Struct struct {
	Greeting string
	Punct    string
	Who      string
}

func (s String) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	fmt.Fprint(w, s)
}

func (s Struct) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	fmt.Fprint(w, s)
}

func main() {
	// your http.Handle calls here
	http.Handle("/string", String("I'm a frayed knot."))
	http.Handle("/struct", &Struct{"Hello", ":", "Gophers!"})
	http.ListenAndServe("localhost:4000", nil)
}