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# 0137. Single Number II

<https://leetcode.com/problems/single-number-ii>

## Description

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**.

## ac

```java
```