Lesson3 - PermMissingElem

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.

Write an efficient algorithm for the following assumptions:

• 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)].

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# you can write to stdout for debugging purposes, e.g.
# print("this is a debug message")

def solution(A):
    A = sorted(A)

    for i in range(0, len(A)):
        if A[i] != i+1:
            return i + 1

    return len(A) + 1