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

Answer 1

wrote this today and got 100/100. not the most elegant solution, but easy to understand -

public int solution(int[] A) {
    int max = A.length;
    int threshold = 1;
    boolean[] bitmap = new boolean[max + 1];

    //populate bitmap and also find highest positive int in input list.
    for (int i = 0; i < A.length; i++) {
        if (A[i] > 0 && A[i] <= max) {
            bitmap[A[i]] = true;
        }

        if (A[i] > threshold) {
            threshold = A[i];
        }
    }

    //find the first positive number in bitmap that is false.
    for (int i = 1; i < bitmap.length; i++) {
        if (!bitmap[i]) {
            return i;
        }
    }

    //this is to handle the case when input array is not missing any element.
    return (threshold+1);
}