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++14 (Clang 3.8.0) (judge verdict: Accepted)

#include <iostream>
#include <algorithm>

using namespace std;

const int NMAX = 3005;
int n, m, k;
char s[NMAX], t[NMAX], a[NMAX];
int dp[NMAX][NMAX];

int main()
{
	//ifstream cin("test.in");
	//ofstream cout("test.out");
	cin >> (s + 1);
	cin >> (t + 1);
	n = strlen(s + 1);
	m = strlen(t + 1);
	for (int i = 1;i <= n;++i)
		for (int j = 1;j <= m;++j)
		{
			if (s[i] == t[j])
				dp[i][j] = dp[i - 1][j - 1] + 1;
			else
				dp[i][j] = max(dp[i - 1][j], dp[i][j - 1]);
		}
	int i = n, j = m;
	k = dp[n][m];
	a[k + 1] = 0;
	while (k > 0)
	{
		if (s[i] == t[j])
		{
			a[k] = s[i];
			--k;
			--i;
			--j;
		}
		else
		{
			if (dp[i - 1][j] > dp[i][j - 1])
				--i;
			else
				--j;
		}
	}
	cout << (a + 1) << "\n";	
	return 0;
}