Print Longest Common Subsequence

public class Solution {
    public static String longestCommonSubsequence(String s1, String s2) {
        int n = s1.length(), m = s2.length();
        int[][] dp = new int[n + 1][m + 1];
 
        // Fill the DP table
        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= m; j++) {
                if (s1.charAt(i - 1) == s2.charAt(j - 1))
                    dp[i][j] = 1 + dp[i - 1][j - 1];
                else
                    dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]);
            }
        }
 
        // Reconstruct the LCS from the table
        StringBuilder lcs = new StringBuilder();
        int i = n, j = m;
        while (i > 0 && j > 0) {
            if (s1.charAt(i - 1) == s2.charAt(j - 1)) {
                lcs.append(s1.charAt(i - 1));
                i--;
                j--;
            } else if (dp[i - 1][j] > dp[i][j - 1]) {
                i--;
            } else {
                j--;
            }
        }
 
        return lcs.reverse().toString(); // because we built it backwards
    }