new_contents: '''
  https://app.codility.com/demo/results/demoHZEZJ5-D8X/
  
  
  
  This is a demo task.
  Write a function:
  
      def solution(A)
  
  that, given an array A of N integers, returns the smallest positive integer (greater than 0) that does not occur in A.
  
  For example, given A = [1, 3, 6, 4, 1, 2], the function should return 5.
  
  Given A = [1, 2, 3], the function should return 4.
  
  Given A = [−1, −3], the function should return 1.
  
  Write an efficient algorithm for the following assumptions:
  
  N is an integer within the range [1..100,000];
  each element of array A is an integer within the range [−1,000,000..1,000,000].
  
  '''
  
  
  # you can write to stdout for debugging purposes, e.g.
  # print("this is a debug message")
  
  def solution(A):
      # write your code in Python 3.6
      pos_set = set()
      for a in A:
          if a > 0:
              pos_set.add(a)
      pos = list(pos_set)
      pos.sort()
  
      res = 1
      for num in pos:
          if res < num:
              break
          else:
              res = num + 1
      return res
subject: Implement MissingInteger (microsoft oa demo)