Codility Lesson 4 MissingInteger Python

Question

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].

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My Answer

def solution(A):
    A = set(sorted(A))
    spi = 1
    for a in A:
        if a <= 0:
            continue
        else:
            if spi == a:
                spi += 1
    return spi