https://codeiq.jp/q/1642

codeiq.rb

#raw_list = STDIN.gets.chomp.split("\n").collect {|item| item.to_i}
raw_list = []
while str = STDIN.gets#.chomp
  break if str.empty?
  raw_list.push str.to_i
end
count_changed = 0

raw_list.each_with_index do |item, index|
  if item != (index + 1) then
    item_index = raw_list.find_index(index + 1)
    raw_list[item_index] = item
    raw_list[index] = index + 1
    count_changed += 1
  end
end

p count_changed