class Solution {
    public int solution(int[] A) {
        int counter[] = new int[A.length];

        // Count the items, only the positive numbers
        for (int i = 0; i < A.length; i++)
            if (A[i] > 0 && A[i] <= A.length)
                counter[A[i] - 1]++;

        // Return the first number that has count 0
        for (int i = 0; i < counter.length; i++)
            if (counter[i] == 0)
                return i + 1;

        // If no number has count 0, then that means all number in the sequence
        // appears so the next number not appearing is in next number after the
        // sequence.
        return A.length + 1;
    }
}