text: # An array A consisting of N different integers is given. The array contains integers in the range [1..(N + 1)], which means that exactly one element is missing.
  #
  # Your goal is to find that missing element.
  #
  # Write a function:
  #
  # def solution(A)
  #
  # that, given an array A, returns the value of the missing element.
  #
  # For example, given array A such that:
  #
  #   A[0] = 2
  #   A[1] = 3
  #   A[2] = 1
  #   A[3] = 5
  # the function should return 4, as it is the missing element.
  #
  # Assume that:
  #
  # N is an integer within the range [0..100,000];
  # the elements of A are all distinct;
  # each element of array A is an integer within the range [1..(N + 1)].
  # Complexity:
  #
  # expected worst-case time complexity is O(N);
  # expected worst-case space complexity is O(1), beyond input storage (not counting the storage required for input arguments).
  
  
  def solution(A):
      num = 1
      hash = set()
  
      for i in A:
          hash.add(i)
  
      while hash.__contains__(num):
          num +=1
      return  num
  
  if __name__ == "__main__":
      A = [1, 3, 6, 4, 1, 2]
  
      print(solution(A))