Check whether array A is a permutation.

PermCheck.java

public class PermCheck {
	public int checkIfIsPermutation(int[] A) {
		if(A == null || A.length == 0) {
			return -1;
		}
		
		int[] passed = new int[A.length];
		for(int i = 0; i < passed.length; i++) {
			passed[i] = -1;
		}
		
		int missing = passed.length;
		
		for(int i = 1; i <= A.length; i++) {
			if(A[i - 1] < 1 || A[i - 1] > A.length) {
				return 0;
			}
			if(passed[A[i - 1] - 1] != -1) {
				return 0;
			} else {
				passed[A[i - 1] -1] = i;
				missing -= 1;
			}
		}
		
		if(missing == 0) {
			return 1;
		}
		
		return 0;
	}
}