# 136.Single-Number

## 136. Single Number

## 题目地址

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

## 题目描述

```
Given a non-empty array of integers, every element appears twice except for one. Find that single one.

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

Example 1:
Input: [2,2,1]
Output: 1

Example 2:
Input: [4,1,2,1,2]
Output: 4
```

## 代码

### Approach #1 List Operation

```java
class Solution {
  public int singleNumber(int[] nums) {
    List<Integer> list = new ArrayList<>();
    for (int i: nums) {
      if (!list.contains(i)) {
        list.add(i);
      } else {
        list.remove(list.indexOf(i));
      }
    }
    return list.get(0);
  }
}
```

### Approach #2 Bit Manipulation

```java
class Solution {
  public int singleNumber(int[] nums) {
    int a = 0;
    for (int i : nums) {
      a ^= i;
    }
    return a;
  }
}
```