Go Tour Excercies

go_tour.go

// Exercise 25 - Loops and Functions
// --------------------------------------------------------------------

package main

import (
	"fmt"
	"math"
)

func Sqrt(x float64) float64 {
	z := 1.0

	for i := 0; i < 10000000; i += 1 {
		z = z - (math.Pow(z, 2) - x) / 2.0*z
	}
	return z
}

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

// => 1.4141017458848133




// Exercise 38 - Slices
// --------------------------------------------------------------------

package main

import "code.google.com/p/go-tour/pic"

func Pic(dx, dy int) [][]uint8 {
    buffer := make([][]uint8, dy)
    
    for y := range buffer {
        buffer[y] = make([]uint8, dx)
        
        for x := range buffer[y] {
            buffer[y][x] = uint8(x) ^ uint8(y)
        }
    }
    
    return buffer
}

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

// => (an image appears on the go tour website)



// Exercise 43 - Maps
// --------------------------------------------------------------------

package main

import (
    "code.google.com/p/go-tour/wc"
    "strings"
)

func WordCount(s string) map[string]int {
    counts := make(map[string]int)
    
    for _, word := range strings.Fields(s) {
        counts[word] += 1
    }
    
    return counts
}

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

// PASS



// Exercise 46 - Fibonacci
// --------------------------------------------------------------------
// TODO: I do not grok this.  So I reverse the for loop to remind myself
// that i is not needed as an argument.  The key point here is that x,y,z
// persist in the closure scope (i think).

package main

import "fmt"

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

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


// Exercise 50 - Complex Cube Roots
// --------------------------------------------------------------------

package main

import (
    "fmt"
    "math/cmplx"
)

func Cbrt(x complex128) complex128 {
    z := complex128(5.0)
    for i := 0; i < 10; i++ {
        z = z - (cmplx.Pow(z, 3) - x) / (3 * (cmplx.Pow(z, 2)))
    }
    
    return z
}

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

}