Go

연습문제만 풀다

Exercise: Loops and Functions

package main

import (
    "fmt"
    "math"
)

func Sqrt(x float64) float64 {
    z := 1.0
    for i := 0; i < 10; i++ {
        z -= (z * z - x) / (2 * z)
    }
    return z
}

func SqrtCount(x float64) (float64, int) {
    z := 1.0
    sqrt := math.Sqrt(x)
    count := 0
    for ; z != sqrt; count++ {
        z -= (z * z - x) / (2 * z)
    }
    return z, count
}

func main() {
    fmt.Printf("Sqrt : %v\n", Sqrt(2))
    fmt.Printf("math.Sqrt : %v\n", math.Sqrt(2))
    value, count := SqrtCount(2)
    fmt.Printf("SqrtCount : %v(%d回ループ)\n", value, count)
}

Sqrt : 1.414213562373095
math.Sqrt : 1.4142135623730951
SqrtCount : 1.4142135623730951(5回ループ)

Exercise: Maps

package main

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

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

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

PASS
 f("I am learning Go!") = 
  map[string]int{"Go!":1, "I":1, "am":1, "learning":1}
PASS
 f("The quick brown fox jumped over the lazy dog.") = 
  map[string]int{"quick":1, "brown":1, "jumped":1, "the":1, "The":1, "over":1, "lazy":1, "dog.":1, "fox":1}
PASS
 f("I ate a donut. Then I ate another donut.") = 
  map[string]int{"another":1, "I":2, "ate":2, "a":1, "donut.":2, "Then":1}
PASS
 f("A man a plan a canal panama.") = 
  map[string]int{"A":1, "man":1, "a":2, "plan":1, "canal":1, "panama.":1}

Exercise: Fibonacci closure

package main

import "fmt"

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

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

0
1
1
2
3
5
8
13
21
34

Exercise: Stringers

package main

import "fmt"

type IPAddr [4]byte

func (i IPAddr) String() string {
    return fmt.Sprintf("%d.%d.%d.%d", i[0], i[1], i[2], i[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)
    }
}

loopback: 127.0.0.1
googleDNS: 8.8.8.8

Exercise: rot13Reader

package main

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

type rot13Reader struct {
    r io.Reader
}

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

    if err != nil {
        return num, err
    }

    for i := 0; i < num; i++ {
        if ('a' <= b[i] && b[i] <= 'm') || ('A' <= b[i] && b[i] <= 'M'){
            b[i] += 13
        } else if ('n' <= b[i] && b[i] <= 'z') || ('N' <= b[i] && b[i] <= 'Z') {
            b[i] -= 13
        }
    }
    return num, err
}

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

You cracked the code!

느끼다