permutation_missing_element.py

"""
Task: PermMissingElem
Goal: Find the missing element in a given permutation
Website: https://app.codility.com/programmers/lessons/3-time_complexity/perm_missing_elem/
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A zero-indexed 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 a zero-indexed 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):
    A.sort()
    N = len(A)
    my_list = list(range(1,N+2))
    
    if N == 0:
        return 1
    else:
        for number in my_list:
            if number not in A:
                return number