# 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;
  }
}
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://wentao-shao.gitbook.io/leetcode/array/136.single-number.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.