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 PHP7 (7.0.15) (judge verdict: Wrong Answer)

<?php
$dirty_s = str_split(fgets(STDIN));
$dirty_t = str_split(fgets(STDIN));
$double_used_words = array_intersect($dirty_s, $dirty_t);
$washed_s = array_intersect($dirty_s, $double_used_words);
$washed_t = array_intersect($dirty_t, $double_used_words);


$dp = [];
foreach ($washed_s as $s_index => $s) {
    foreach ($washed_t as $t_index => $t) {

        if ($t === $s) {
            $new = $dp[$s_index][$t_index - 1] + 1;
            $old = $dp[$s_index - 1][$t_index];
            $dp[$s_index][$t_index] = max($new, $old);
        } else {
            $new = $dp[$s_index][$t_index - 1];
            $old = $dp[$s_index - 1][$t_index];
            $dp[$s_index][$t_index] = max($new, $old);
        }
    }
}

$answer='';
foreach (end($dp) as $index => $value) {
    if($index==1&&$value==1||$value-$dp[$index-1]=1){
        $answer .= $washed_s[$index];
    }
}
if($answer==''){echo' ';}else{echo $answer;}