PermCheck.java

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