Problem:
Score : 100 points

Problem Statement

You are given strings s and t.
Find one longest string that is a subsequence of both s and t.

Notes

A subsequence of a string x is the string obtained by removing zero or more characters from x and concatenating the remaining characters without changing the order.

Constraints

s and t are strings consisting of lowercase English letters.

1 \leq |s|, |t| \leq 3000

Input

Input is given from Standard Input in the following format:

s
t

Output

Print one longest string that is a subsequence of both s and t.
If there are multiple such strings, any of them will be accepted.

Sample Input 1

axyb
abyxb

Sample Output 1

axb

The answer is axb or ayb; either will be accepted.

Sample Input 2

aa
xayaz

Sample Output 2

aa

Sample Input 3

a
z

Sample Output 3

The answer is (an empty string).

Sample Input 4

abracadabra
avadakedavra

Sample Output 4

aaadara

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace CSharp_AtCoder
{

    
    class Program
    {      

        static void Main(string[] args)
        {
            string S = Console.ReadLine();
            string T = Console.ReadLine();

            int sn = S.Length;
            int tn = T.Length;
            // dp[i, j] := SのsnまでとTのtnまで文字列のLCS
            int[,] dp = new int[sn + 1, tn + 1];
            

            for(int i = 1; i <= sn; i++)
            {
                for(int j = 1; j <= tn; j++)
                {
                    if(S[i - 1] == T[j - 1])
                    {
                        dp[i, j] = dp[i - 1, j - 1] + 1;
                    }
                    else
                    {
                        dp[i, j] = Math.Max(dp[i, j - 1], dp[i - 1, j]);
                    }
                }
            }

            //復元
            string lcs = "";
            int si = sn;
            int ti = tn;
            while(si > 0 && ti > 0)
            {
                if(S[si - 1] == T[ti - 1])
                {
                    lcs = S[si - 1] + lcs;
                    si--;
                    ti--;
                }
                else
                {
                    if (dp[si, ti] == dp[si - 1, ti]) si--;
                    else ti--;
                }
            }

            Console.WriteLine(lcs);
            
        }
    }
}