712.cpp

        vector<vector<int> > C(s1.length() + 1, vector<int>(s2.length() + 1, 0));
        // initial
        for (int i = 1; i < s2.length() + 1; ++i) {
            C[0][i] = C[0][i - 1] + s2[i - 1];
        }
        for (int i = 1; i < s1.length() + 1; ++i) {
            C[i][0] = C[i - 1][0] + s1[i - 1];
        }
        for (int i = 1; i < s1.length() + 1; ++i) {
            for (int j = 1; j < s2.length() + 1; ++j) {
                if (s1[i - 1] == s2[j - 1]) {
                    C[i][j] =  C[i - 1][j - 1];
                } else {
                    // delete s1[i-1] or s2[j-1]
                    C[i][j] = min(C[i - 1][j] + s1[i - 1], C[i][j - 1] + s2[j - 1]);
                }
            }
        }
        return C[s1.length()][s2.length()];