https://scrapbox.io/kou029w/2017-10-12_%E7%AB%B6%E6%8A%80%E3%83%97%E3%83%AD%E3%82%B0%E3%83%A9%E3%83%9F%E3%83%B3%E3%82%B0%E3%82%84%E3%81%A3%E3%81%A6%E3%81%BF%E3%81%9F_%E7%B7%B4%E7%BF%92%E7%B7%A8

.keep

ruby -v
ruby 2.3.1p112 (2016-04-26) [x86_64-linux-gnu]

while str = STDIN.gets
end

これで標準入力が取得できるんだ...知らなかった

n, c = STDIN.gets.split(' ').map(&:to_i)

l=[]

while i = STDIN.gets
  l << i.to_i
end

l.delete_if {|i| i > c }

sum = 0
l.each {|i| sum += (i == c || i + 1 == c ? 1 : 0) }.delete_if {|i| i == c || i + 1 == c }

l.sort!
while i = l.pop
  sum+=1
  l.each do|j|
    if i + j + 1 <= c
      l-=[j]
      break
    end
  end
end

puts sum

1時間50分もかかった

間違えてた

n, c = STDIN.gets.split(' ').map(&:to_i)

l=[]

while i = STDIN.gets
  l << i.to_i
end

sum = 0
l.each {|i| sum += (i == c || i + 1 == c ? 1 : 0) }.delete_if {|i| i == c || i + 1 == c }

l.sort!
while i = l.pop
  sum+=1
  l.each_with_index do |j,ix|
    if i + j + 1 <= c
      l.delete_at(ix)
      break
    end
  end
end

puts sum

TLEだ

整理した

n, c = STDIN.gets.split(' ').map(&:to_i)

sum = 0
l = STDIN.read.split("\n").map(&:to_i).each {|i| sum += (i == c || i + 1 == c ? 1 : 0) }.delete_if {|i| i == c || i + 1 == c }.sort

while i = l.pop
  sum+=1
  l.each_with_index do |j,ix|
    if i + j + 1 <= c
      l.delete_at(ix)
      break
    end
  end
end

puts sum