Solution

• 拼接再截取

class Solution {
public:
    string LeftRotateString(string str, int n) {
        int len = str.size();
        if (len == 0 || n <= 0) return str;
        n %= len;
        str += str;  // !循环问题，拼接
        return str.substr(n, len);
    }
};

• 截取再重排

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