LCS.cpp

string lcs(string s, string ss)
{
    int m = s.size();
    int n = ss.size();
    vector<vector<int>> dp(m + 1, vector<int>(n + 1, 0));

    for (int i = 1; i <= m; i++)
    {
        for (int j = 1; j <= n; j++)
        {
            if (s[i - 1] == ss[j - 1])
                dp[i][j] = dp[i - 1][j - 1] + 1;
            else
                dp[i][j] = max(dp[i - 1][j], dp[i][j - 1]);
        }
    }

    // return dp[m][n]; // if you want the length of LCS

    // reconstruction of subsequence
    string ans = "";
    int i = m, j = n;
    while (i > 0 and j > 0)
    {
        if (s[i - 1] == ss[j - 1])
        {
            ans += s[i - 1];
            i--, j--;
        }
        else if (dp[i - 1][j] > dp[i][j - 1])
            i--;
        else
            j--;
    }
    reverse(all(ans));
    return ans; // if you want the LCS string
}