Question

Given a non-empty array of integers, every element appears three times except for one, which appears exactly once. Find that single one.

Note:

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

Example 1:

Input: [2,2,3,2] Output: 3

Example 2:

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

Difficulty:Medium

Category:Bit Manipulation

Analyze

Solution

class Solution {
 public:
  int singleNumber(vector<int>& nums) {
    int res = 0;
    const int len_int = sizeof(int) * 8;
    int count[len_int];
    fill_n(&count[0], len_int, 0);

    for (int i = 0; i < nums.size(); ++i) {
      for (int j = 0; j < len_int; ++j) {
        count[j] += (nums[i] >> j) & 1;
      }
    }
    for (int i = 0; i < len_int; ++i) {
      res += ((count[i] % 3) << i);
    }
    return res;
  }
};