LCS.cpp

#include <bits/stdc++.h>
using namespace std;

int main() {
    string s1, s2;
    cin >> s1 >> s2;

    int n = s1.size();
    int m = s2.size();

    vector<vector<int>> dp(n + 1, vector<int>(m + 1, 0));

    // Build DP Table
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {

            if (s1[i - 1] == s2[j - 1])
                dp[i][j] = 1 + dp[i - 1][j - 1];
            else
                dp[i][j] = max(dp[i - 1][j], dp[i][j - 1]);
        }
    }

    // Print length of LCS
    cout << "LCS length = " << dp[n][m] << endl;

    // Reconstruct LCS (optional but useful)
    string lcs = "";
    int i = n, j = m;

    while (i > 0 && j > 0) {
        if (s1[i - 1] == s2[j - 1]) {
            lcs += s1[i - 1];
            i--;
            j--;
        } else if (dp[i - 1][j] > dp[i][j - 1]) {
            i--;
        } else {
            j--;
        }
    }

    reverse(lcs.begin(), lcs.end());
    cout << "LCS = " << lcs << endl;

    return 0;
}