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 Ruby (2.3.3) (judge verdict: Time Limit Exceeded)

s_orig = gets.chomp
t_orig = gets.chomp

s = s_orig.codepoints
t = t_orig.codepoints

dp = Array.new(s.length+1) { Array.new(t.length+1,0) }

0.upto(s.length-1).each do |i|
  0.upto(t.length-1).each do |j|
    if s[i] == t[j]
      dp[i+1][j+1] = dp[i][j] + 1
    else
      dp[i+1][j+1] = dp[i+1][j] > dp[i][j+1] ? dp[i+1][j] : dp[i][j+1]
    end
  end
end

ans = ''
current = dp[s.length][t.length]
y = s.length
x = t.length

while true
  if current == 0
    break
  elsif dp[y-1][x] == current
    y-=1
  elsif dp[y][x-1] == current
    x-=1
  else
    # p [y,x,current]
    y-=1
    x-=1
    ans += s_orig[y]
    current-=1
  end
end

# dp.each{|l| p l}

puts ans.reverse