---
title: 'LeetCode 136. Single Number'
disqus: hackmd
---

# LeetCode 136. Single Number

## Description

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

You must implement a solution with a linear runtime complexity and use only constant extra space.

## Example

Input: nums = [2,2,1]
Output: 1

## Constraints

1 <= nums.length <= 3 * 10^4^
-3 * 10^4^ <= nums[i] <= 3 * 10^4^
Each element in the array appears twice except for one element which appears only once.

## Answer

此題因為每個數有重複的話只有重複兩次，所以做兩次XOR就會回復原本的，照XOR的特點從頭做到XOR到尾就可以抓出不重複的那一個。

// 2021_11_04
int singleNumber(int* nums, int numsSize) {
    int i = 0, ans = *nums++;
    for(i = 1;i < numsSize;i++,nums++){
        ans ^= *nums;
    }
    return ans;
}

## Link
https://leetcode.com/problems/single-number/
###### tags: `Leetcode`