Common Child

• Time : O(nm)
• Space : O(nm)

int commonChild(string A, string B) {
    int n = A.length(), m = B.length();
    vector<vector<int>> dp(n + 1, vector<int>(m + 1));
    for(int i = 1; i <= n; i++) {
        for(int j = 1; j <= m; j++) {
            if(A[i-1] == B[j-1]) dp[i][j] = 1 + dp[i-1][j-1];
            else dp[i][j] = max(dp[i-1][j], dp[i][j-1]);
        }
    }
    return dp[n][m];
}