一、题目

Given an integer array nums where every element appears three times except for one, which appears exactly once. Find the single element and return it.

You must implement a solution with a linear runtime complexity and use only constant extra space.

Example 1:

Input: nums = [2,2,3,2]
Output: 3
Example 2:

Input: nums = [0,1,0,1,0,1,99]
Output: 99

Constraints:

1 <= nums.length <= 3 * 104
-231 <= nums[i] <= 231 - 1
Each element in nums appears exactly three times except for one element which appears once.

二、题解

class Solution {
public:int singleNumber(vector<int>& nums) {int n = nums.size();//记录所有数每一位上为1的总数vector<int> cnt(32,0);for(auto x:nums){for(int i = 0;i < 32;i++){cnt[i] += (x >> i) & 1;}}int res = 0;for(int i = 0;i < 32;i++){//不是3的倍数，说明该数在这一位上为1if(cnt[i] % 3 != 0) res |= 1 << i;}return res;}
};