LCS.java

public class LCS {
    public static int lcs(String a, String b) {
        int n = a.length(), m = b.length();
        int[][] dp = new int[n + 1][m + 1];

        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= m; j++) {
                if (a.charAt(i - 1) == b.charAt(j - 1)) {
                    dp[i][j] = dp[i - 1][j - 1] + 1;
                } else {
                    dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]);
                }
            }
        }
        return dp[n][m];
    }

    public static String getLCS(String a, String b) {
        int n = a.length(), m = b.length();
        int[][] dp = new int[n + 1][m + 1];

        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= m; j++) {
                if (a.charAt(i - 1) == b.charAt(j - 1)) dp[i][j] = dp[i - 1][j - 1] + 1;
                else dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]);
            }
        }

        StringBuilder sb = new StringBuilder();
        int i = n, j = m;
        while (i > 0 && j > 0) {
            if (a.charAt(i - 1) == b.charAt(j - 1)) {
                sb.append(a.charAt(i - 1));
                i--; j--;
            } else if (dp[i - 1][j] > dp[i][j - 1]) i--;
            else j--;
        }
        return sb.reverse().toString();
    }

    public static void main(String[] args) {
        String a = "AGGTAB";
        String b = "GXTXAYB";
        System.out.println("LCS length: " + lcs(a, b));
        System.out.println("LCS: " + getLCS(a, b));
    }
}