# 文档更新说明

• 最后更新 2018年03月05日
• 首次更新 2017年05月16日

# 前言

使用Swift语言完成LetCode题目,就不多介绍了.

# 561. Array Partition I

Given an array of 2n integers, your task is to group these integers into n pairs of integer, say (a1, b1), (a2, b2), …, (an, bn) which makes sum of min(ai, bi) for all i from 1 to n as large as possible.

## Example1

Input: [1,4,3,2]
Output: 4
Explanation: n is 2, and the maximum sum of pairs is 4.


## Note

1. n is a positive integer, which is in the range of [1, 10000].
2. All the integers in the array will be in the range of [-10000, 10000].

see. 推导方法

# 461. Hamming Distance

The Hamming distance between two integers is the number of positions at which the corresponding bits are different.

Given two integers x and y, calculate the Hamming distance.

## Example1

Input: x = 1, y = 4

Output: 2

Explanation:
1   (0 0 0 1)
4   (0 1 0 0)
↑   ↑
The above arrows point to positions where the corresponding bits are different.


0 ≤ x, y < 2^31.

## Solution

先将x和y做异或运算,再统计得到的二进制数字里面有多少个1(采用清1法统计)

# 7. Reverse Integer

Given a 32-bit signed integer, reverse digits of an integer.

## Example1

Input: 123
Output:  321


## Example2

Input: -123
Output:  -321


## Example3

Input: 120
Output:  21


分成正负数处理,速度最快.