136. Single Number

Given an array of integers, every element appears twice except for one. Find that single one.

Note: Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

a ^ b = b ^ a;

0 ^ a = a;

public int singleNumber(int[] nums) { if (nums == null || nums.length == 0) return 0; int res = nums[0]; for (int i = 1; i < nums.length; i++) { res ^= nums[i]; } return res; }