Missing integer variation - O(n) solution needed [closed]

Answer 1

This is my solution using python:

def solution(A):
    m = max(A)

    if m <= 0:
        return 1

    if m == 1:
        return 2

    # Build a sorted list with all elements in A
    s = sorted(list(set(A)))

    b = 0

    # Iterate over the unique list trying to find integers not existing in A
    for i in xrange(len(s)):
        x = s[i]

        # If the current element is lte 0, just skip it
        if x <= 0:
            continue;

        b = b + 1

        # If the current element is not equal to the current position,
        # it means that the current position is missing from A
        if x != b:
            return b

    return m + 1

Scored 100%/100% https://codility.com/demo/results/demoDCU7CA-SBR/