代码

class Solution {
    public String leftRotateString(String str, int n) {
        char[] s = str.toCharArray();
        for(int i = 0, j = s.length - 1; i < j; i++, j--){
            swap(s,i,j);
        }
        for (int i = 0, j = s.length - n - 1; i < j; i++, j--){
            swap(s,i,j);
        }
        for (int i = s.length - n , j = s.length - 1; i < j; i++, j--){
            swap(s,i,j);
        }
        String res = "";
        for (char c : s){
            res += c;
        }
        return res;
    }
    public void swap(char[] s, int i, int j){
        char temp = s[i];
        s[i] = s[j];
        s[j] = temp;
    }
    //使用工具类搞面试官心态
     public String leftRotateString(String str, int n) {
        return str.substring(n, str.length()) + str.substring(0,n);
    }
}