problem4.rb

# http://www.softantenna.com/wp/software/5-programming-problems/
# https://blog.svpino.com/2015/05/07/five-programming-problems-every-software-engineer-should-be-able-to-solve-in-less-than-1-hour
#
# 問題4
# 正の整数のリストを与えられたとき、数を並び替えて可能な最大数を返す関数を記述せよ。
# 例えば、[50, 2, 1, 9]が与えられた時、95021が答えとなる(解答例)。

#@list = [50, 2, 1, 9]
@list = [50, 2, 1, 9, 95, 83]
@result_all = []

# @param [Array] list
def func1(list)
  create_all_combinations(list, [])
  max = -1
  @result_all.each do |candidate|
    val_string = candidate.reduce('') {|result, num|
      result + "#{num}"
    }
    val = val_string.to_i
    max = val if val > max
  end
  max
end

def create_all_combinations(list, result)
  # p "list = #{list}"
  # p "result = #{result}"
  if list.empty?
    @result_all.push(result)
    return
  end
  list.each do |val|
    create_all_combinations(list.reject {|v| v == val}, [result, val].flatten)
  end
end


max = func1(@list.dup)
p "result = #{@result_all}"
p "max = #{max}"