137. Single Number II

• Difficulty: Medium

• Topics: Bit Manipulation

• Similar Questions:

  • Single Number

  • Single Number III

Problem:

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

Solutions:

class Solution {
public:
    int singleNumber(vector<int>& nums) {
        int ones = 0;
        int tens = 0;

        for (auto num : nums) {
            ones = ones ^ num;

            int carry = (~ones) & num;
            tens = tens ^ carry;

            int mask = ones & tens;
            ones = ones & (~mask);
            tens = tens & (~mask);
        }

        return ones;
    }
};