Single Number

bit manipulation

public class Solution {
    public int singleNumber(int[] A) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(A == null || A.length == 0)
            return 0;
        int result = 0;
        for(int i : A)
            result ^= i;
        return result;
    }
}