Single Number II

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.

Test Cases

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 * 10<sup>4</sup>

• -2<sup>31</sup> <= nums[i] <= 2<sup>31</sup> - 1

• Each element in nums appears exactly three times except for one element which appears once.

Solution

C C++ Java

int singleNumber(int* nums, int size) {
    int ones = 0, twos = 0;
    for(int i=0; i<size; i++) {
        ones = (ones ^ nums[i]) & ~twos;
        twos = (twos ^ nums[i]) & ~ones;
    }
    return ones;
}

class Solution {
public:
    int singleNumber(vector<int>& nums) {
        int ones = 0, twos = 0;
        for(int i=0; i<nums.size(); i++) {
            ones = (ones ^ nums[i]) & ~twos;
            twos = (twos ^ nums[i]) & ~ones;
        }
        return ones;
    }
};

class Solution {
    public int singleNumber(int[] nums) {
        int ones = 0, twos = 0;
        for (int num : nums) {
            ones = (ones ^ num) & ~twos;
            twos = (twos ^ num) & ~ones;
        }
        return ones;
    }

}