136. Single Number

Given a non-empty 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?

Example 1:

Input: [2,2,1]
Output: 1

Example 2:

Input: [4,1,2,1,2]
Output: 4

// XOR Bit Manipulation
int singleNumber(vector<int>& nums) { // time: O(n); space: O(1)
    int res = 0;
    for (int i = 0; i < nums.size(); ++i) {
        res ^= nums[i];
    }
    return res;
}