MissingInteger

Write a function:

class Solution { public int solution(int[] 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].



**************************************** solution ****************************************

function solution($A)
{
    sort($A);
    $min = 1;

    foreach ($A as $inner) {
        if ($inner == $min) {
            $min++;
        }
    }

    return $min;
}