左旋转字符串

题目：定义字符串的左旋转操作：把字符串前面的若干个字符移动到字符串的尾部。如把字符串abcdef左旋转2位得到字符串cdefab。请实现字符串左旋转的函数。

给出两种方法，第二种方法很巧妙....

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//左旋转字符串

#include<iostream>

#include<string>

using namespace std;

bool shiftWithStl(string &s,int len){

    if(len<0||len>s.length()) return false;

    string temp=s.substr(0,len);        //取0位置开始len个字符的子串

    s.erase(0,len);                     //删除0位置开始len个字符的子串

    s.append(temp);                     //追加

    return true;

}

bool shiftSelf(string &s,int len){         //好方法....三次翻转实现

    cout<<s<<endl;

    if(len<0||len>s.length()) return false;

    int start=0;

    int mid=len-1;

    int end=s.length()-1;

    void reverseString(string &,int,int);

    reverseString(s,start,mid);           

    //cout<<s<<endl;

    reverseString(s,mid+1,end);        //mid+1

    //cout<<s<<endl;

    reverseString(s,start,end);

    //cout<<s<<endl;

    return true;

}

void reverseString(string &s,int start,int end){

    while(start<end){                     //翻转字符串

        char temp;

        temp=s[start];

        s[start]=s[end];

        s[end]=temp;

        start++;

        end--;

    }

}

int main(void){

    string s1="abcdef";

    string s2="abcdef";

    if(shiftWithStl(s1,2)) cout<<s1<<endl;

    else cout<<"error"<<endl;

    if(shiftSelf(s2,2)) cout<<s2<<endl;

    else cout<<"error"<<endl;

    system("pause");

    return 0;

}