# 137. Single Number II

## Problem

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:

- $1 <= nums.length <= 3 * 10^4$
- $-2^{31} <= nums[i] <= 2^{31} - 1$
- Each element in nums appears exactly three times except for one element which appears once.

## Code

```
class Solution {
public int singleNumber(int[] nums) {
int ones = 0;
int twos = 0;
for(int i = 0; i < nums.length; i++){
ones = (ones ^ nums[i]) & ~twos;
twos = (twos ^ nums[i]) & ~ones;
}
return ones;
}
}
```

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