Go程序设计语言练习题-第4章

4.3~4.7

package main

import (
    "fmt"
    "unicode"
    "unicode/utf8"
    "unsafe"
)

// 4.3 重写reverse函数，使用数组指针作为参数而不是slice
// ?数组长度是类型的一部分
func reverse(arr *[5]int) {
    length := len(*arr)
    for i, j := 0, length-1; i < j; i, j = i+1, j-1 {
        (*arr)[i], (*arr)[j] = (*arr)[j], (*arr)[i]
    }
}

// 4.4 编写函数rotate，实现一次遍历就可以完成元素旋转
func rotate(s []int) {

}

// 4.5 编写一个就地处理函数，用于去除[]string slice中相邻重复字符串元素
func distinct(s []string) []string {
    dist := s[0:1]
    for i := 1; i < len(s); i++ {
        for s[i] != dist[len(dist)-1] {
            dist = append(dist, s[i])
        }
    }
    return dist
}

// 4.6 编写一个就地处理函数，用于将一个UTF-8编码的字节slice中所有相邻的Unicode空白字符（查看unicode.IsSpace）缩减为一个ASCII空白字符。
func ex4_6(b []byte) []byte {
    var i int
    for i, l := 0, 0; l < len(b); {
        r, size := utf8.DecodeRune(b[i:])
        l += size
        if unicode.IsSpace(r) {
            if i > 0 && b[i-1] == byte(32) {
                copy(b[i:], b[i+size:])
            } else {
                b[i] = byte(32)
                copy(b[i+1:], b[i+size:])
                i++
            }
        } else {
            i += size
        }
    }
    return b[0:i]
}

// 4.7 修改函数reverse，来反转一个UTF-8编码字符串中的字符元素，传入参数是该字符串对应的字节slice类型（[]byte）。是否可以做到不重新分配内存就实现该功能。
func mbreverse(b []byte) []byte {
    var res []byte
    for i := len(b); i > 0; {
        r, size := utf8.DecodeLastRune(b[:i])
        res = append(res, []byte(string(r))...)
        i -= size4
    }
    return res
}

func main() {
    // 4.3
    arr := [...]int{1, 2, 3, 4, 5}
    reverse(&arr)
    fmt.Println(arr)

    // 4.5
    s := []string{" ", " ", "aaa", " ", "bbb", "bbb", "c", "d", "d"}
    dist := distinct(s)
    fmt.Printf("原slice的底层数组地址：%p\n", unsafe.Pointer(uintptr(unsafe.Pointer(&s))))
    fmt.Printf("原slice的len：%d\n", *(*int)(unsafe.Pointer(uintptr(unsafe.Pointer(&s)) + unsafe.Sizeof(&s))))
    fmt.Printf("原slice的cap：%d\n", *(*int)(unsafe.Pointer(uintptr(unsafe.Pointer(&s)) + 2*unsafe.Sizeof(&s))))

    fmt.Printf("去重后底层数组地址：%p\n", unsafe.Pointer(uintptr(unsafe.Pointer(&dist))))
    fmt.Printf("len:%d\n", *(*int)(unsafe.Pointer(uintptr(unsafe.Pointer(&dist)) + unsafe.Sizeof(&dist))))
    fmt.Printf("cap:%d\n", *(*int)(unsafe.Pointer(uintptr(unsafe.Pointer(&dist)) + 2*unsafe.Sizeof(&dist))))

    // 4.6
    b := []byte("北京\t欢迎\n您")
    fmt.Printf("%s\n%v\n", b, b)
    ex4_6(b)
    fmt.Printf("%s\n%v\n", b, b)

    // 4.7
    b = []byte("北京欢迎您welcome")
    fmt.Printf("%s\n", b)
    fmt.Printf("%s\n", mbreverse(b))

}

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