bool isInterleaving(string &str1, string &str2, string &str3) {

    int n = str1.length();

    int m = str2.length();

    int k = str3.length();

    if (n + m != k) return false;

    vector<vector<bool> > dp(n+1);

    for (int i = 0; i < n+1; i++) {

        dp[i].resize(m+1);

    }

    dp[0][0] = true;

    for (int i = 0; i <= n; i++) {

        for (int j = 0; j <= m; j++) {

            if (i == 0 && j == 0) {

                dp[0][0] = true;

            } else if (i == 0) {

                dp[0][j] = dp[0][j-1] && str2[j-1] == str3[j-1];

            } else if (j == 0) {

                dp[i][0] = dp[i-1][0] && str1[i-1] == str3[i-1];

            } else {

                dp[i][j] = (dp[i-1][j] && str1[i-1] == str3[i+j-1])

                            || (dp[i][j-1] && str2[j-1] == str3[i+j-1]);

            }

        }

    }

    return dp[n][m];

}