Scramble String

class Solution {
public:
    bool isScramble(string s1, string s2) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        int len = s1.length();
        if (len != s2.length()) return false;
        bool ret[len][len][len];
        for (int i = 0; i < len; i++) {
            for (int j = 0; j < len; j++) {
                ret[i][j][0] = (s1[i] == s2[j]);
            }
        }

        for (int l = 2; l <= len; l++) {
            for (int i = 0; i <= len - l; i++) {
                for (int j = 0; j <= len - l; j++) {
                    ret[i][j][l - 1] = false;
                    for (int k = 1; k < l; k++) {
                        if ((ret[i][j][k - 1] && ret[i + k][j + k][l - k - 1]) || 
                            (ret[i][j + l - k][k - 1] && ret[i + k][j][l - k - 1])) {
                            ret[i][j][l - 1] = true;
                            break;
                        }
                    }
                }
            }
        }

        return ret[0][0][len - 1];
    }

};