Submission #7266472

---

Source Code Expand

n = read_line.to_i
a = Array.new(n) { read_line.split.map { |v| v.to_i - 1 }.reverse }
ans = 0
update = Array.new(n) { |i| i }
time = Array.new(n, -1)
while !update.empty?
  n = [] of Int32
  update.each do |i|
    next if a[i].empty?
    next if time[i] == ans
    p = a[i][-1]
    next if time[p] == ans
    if a[p][-1] == i
      n << i
      n << p
      a[i].pop
      a[p].pop
      time[i] = time[p] = ans
    end
  end
  update = n
  ans += 1
end
puts a.all? { |p| p.empty? } ? ans : -1

Submission Info

Judge Result