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 (GCC 5.4.1) (judge verdict: Accepted)

#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<map>
#define _USE_MATH_DEFINES
#include<math.h>
#include<queue>
#include<deque>
#include<stack>
#include<cstdio>
#include<utility>
#include<set>
#include<list>
#include<cmath>
#include<stdio.h>
#include<string.h>
#include<iomanip>
#include<cstdio>
#include<cstdlib>
#include<cstring>
using namespace std;
#define FOR(i, a, b) for (ll i = (a); i <= (b); i++)
#define REP(i, n) FOR(i, 0, n - 1)
#define NREP(i, n) FOR(i, 1, n)
using ll = long long;
using pii = pair<int, int>;
using piii = pair<pii, pii>;
const ll dx[4] = { 0,1,0,-1 };
const ll dy[4] = { -1, 0, 1,0 };
const int INF = 1e9 + 7;
int gcd(int x, int y) {
	if (x < y)swap(x, y);
	if (y == 0)return x;
	return gcd(y, x%y);
}
void mul(ll a, ll b) {
	a = a * b % INF;
}
double mysqrt(double x) {
	double l = 0, r = x;
	for (int i = 0; i < 64; ++i) {
		double m = (l + r) / 2.0;
		if (m*m < x)l = m;
		else r = m;
	}
	return l;
}
///////////////////////////////////////

int dp[3010][3010];
//dp[i][j]でsのi文字目までtのj文字目まで見た時に
int main() {
	//まず最長の物の長さを求める
	string s, t; cin >> s >> t;
	memset(dp, 0, sizeof(dp));
	for (int i = 0; i < s.size(); ++i) {
		for (int j = 0; j < t.size(); ++j) {
			if (s[i] == t[j]) {
				dp[i + 1][j + 1] = dp[i][j] + 1;
			}
			else {
				dp[i + 1][j + 1] = max(dp[i][j + 1], dp[i + 1][j]);
			}
		}
	}
	string ans = "";
	int i = s.size(), j = t.size();
	while (i > 0 && j > 0) {
		if (dp[i][j] == dp[i - 1][j]) {
			--i;
		}
		else if (dp[i][j] == dp[i][j - 1]) {
			--j;
		}
		else {
			ans = s[i - 1] + ans;
			--i, --j;
		}
	}
	cout << ans << endl;
	return 0;
}