左旋转字符串

public class Solution {
    public String LeftRotateString(String str,int n) {
        if(n>=str.length())return str;
        char[] ch = str.toCharArray();
        int len = ch.length-1;
        reverse(ch, 0, n-1);
        reverse(ch, n, len);
        reverse(ch, 0, len);
        return new String(ch);
    }
    public void swap(char[] ch, int i, int j) {
        char temp = ch[i];
        ch[i] = ch[j];
        ch[j] = temp;
    }
    public void reverse(char[] ch, int i, int j) {
        while(i<j)
            swap(ch, i++, j--);
    }
}

class Solution {
public:
    string LeftRotateString(string str, int n) {
        int len = str.length();
        if(len == 0) return "";
        n = n % len;
        str += str;
        return str.substr(n, len);
    }
};