Find the missing element in a given permutation.

PermMissingElem.java

public class PermMissingElem {
	
	 public int findMissingElement(int[] A) {
		 if(A == null || A.length == 0) {
			 return 1;
		 }
		 
		 long N = A.length + 1;
		 long total = N * (N + 1) / 2;
		 
		 long sum = 0L;
		 for(int i = 0; i < A.length; i++) {
			 sum += A[i];
		 }
		 
		 return (int) (total - sum);
	 }
}