[日常] 算法-旋转字符串-三步翻转法

#include <stdio.h>
#include <string.h>
void ReverseString(char* s,int from,int to) 
{
    while (from < to) 
    {   
        char t = s[from];
        s[from++] = s[to];
        s[to--] = t;
    }   
}
void LeftRotateString(char* s,int n,int m)
{
    m %= n;               //若要左移动大于n位，那么和%n 是等价的
    ReverseString(s, 0, m - 1); //反转[0..m - 1]，套用到上面举的例子中，就是X->X^T，即 abc->cba
    ReverseString(s, m, n - 1); //反转[m..n - 1]，例如Y->Y^T，即 def->fed
    ReverseString(s, 0, n - 1); //反转[0..n - 1]，即如整个反转，(X^TY^T)^T=YX，即 cbafed->defabc。
}
int main(){

        char a[]="hello world";
        LeftRotateString(a,strlen(a),2);
        printf("%s\n",a);
}

package main
import(
        "fmt"
)
func ReverseString(s []byte,from int,to int){
        for{
                t:=s[from]
                s[from]=s[to]
                s[to]=t
                from++
                to--
                if from>to{
                        break
                }

        }
}
func LeftRotateString(s []byte,n int,m int){
        m%=n
        ReverseString(s,0,m-1)
        ReverseString(s,m,n-1)
        ReverseString(s,0,n-1)
}

func main(){

        a:=[]byte("hello world")
        LeftRotateString(a,len(a),2)
        fmt.Println(string(a))

}

<?php
function ReverseString(&$str,$from,$to){
        while($from<$to){
                $t=$str[$from];
                $str[$from++]=$str[$to];
                $str[$to--]=$t;
        }   
}
function LeftRotateString(&$str,$n,$m){
        $m%=$n;//如果转换前几个字符的长度比字符串长度大
        ReverseString($str,0,$m-1);
        ReverseString($str,$m,$n-1);
        ReverseString($str,0,$n-1);
}
$a="hello world";
LeftRotateString($a,strlen($a),2);
echo $a."\n";