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?

0和2个相同的数异或等于0  

int singleNumber(int* nums, int numsSize) {
    int flag = 0;
    int i;
    for(i = 0; i < numsSize; i++)
        flag ^= nums[i];
    return flag;
}