#! /usr/bin/env ruby
require 'set'
module Solution
  extend self
  def lcs(arr)
    s = arr.to_set
    max_len = 1
    arr.each do |item|
      len = 1
      low = item - 1
      while s.delete?(low) do
        len = len + 1
        low = low - 1
      end
      high = item + 1
      while s.delete?(high) do
        len = len + 1
        high = high + 1
      end
      max_len = len if len > max_len
    end
    max_len
  end
end