MissingInteger.java

class Solution {
    public int solution(int[] A) {
        int min = A.length + 1;
        int length = A.length;
        boolean[] appearance = new boolean[length];
        for (int i = 0; i < length; i++) {
            if (A[i] > 0 && A[i] <= length) {
                appearance[A[i]-1] = true;
            }
        }
        for (int i = 0; i < length; i++) {
            if (!appearance[i]) {
                min = i + 1;
                break;
            }
        }
        return min;
    }
}