LeetCode C++ 136. Single Number【位操作】簡單

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

題目：找出只出現過一次的數字。

思路：可以用哈希表索引計數；或者排序，從頭開始搜索；最簡單的方法是異或。

代碼：

class Solution {
public:
    int singleNumber(vector<int>& nums) {
        int ans = 0;
        for (auto &i : nums) ans ^= i;
        return ans;
    }
};