[1601. Maximum Number of Achievable Transfer Requests](https://leetcode.com/problems/maximum-number-of-achievable-transfer-requests/)
### 題目描述
We have `n` buildings numbered from `0` to `n - 1`. Each building has a number of employees. It's transfer season, and some employees want to change the building they reside in.
You are given an array `requests` where `requests[i] = [fromi, toi]` represents an employee's request to transfer from building `fromi` to building `toi`.
**All buildings are full**, so a list of requests is achievable only if for each building, the **net change in employee transfers is zero**. This means the number of employees **leaving** is **equal** to the number of employees **moving in**. For example if `n = 3` and two employees are leaving building `0`, one is leaving building `1`, and one is leaving building `2`, there should be two employees moving to building `0`, one employee moving to building `1`, and one employee moving to building `2`.
Return *the maximum number of achievable requests.*
### 範例
**Example 1:**
![](https://assets.leetcode.com/uploads/2020/09/10/move1.jpg =80%x)
```
Input: n = 5, requests = [[0,1],[1,0],[0,1],[1,2],[2,0],[3,4]]
Output: 5
Explantion: Let's see the requests:
From building 0 we have employees x and y and both want to move to building 1.
From building 1 we have employees a and b and they want to move to buildings 2 and 0 respectively.
From building 2 we have employee z and they want to move to building 0.
From building 3 we have employee c and they want to move to building 4.
From building 4 we don't have any requests.
We can achieve the requests of users x and b by swapping their places.
We can achieve the requests of users y, a and z by swapping the places in the 3 buildings.
```
**Example 2:**
![](https://assets.leetcode.com/uploads/2020/09/10/move2.jpg =80%x)
```
Input: n = 3, requests = [[0,0],[1,2],[2,1]]
Output: 3
Explantion: Let's see the requests:
From building 0 we have employee x and they want to stay in the same building 0.
From building 1 we have employee y and they want to move to building 2.
From building 2 we have employee z and they want to move to building 1.
We can achieve all the requests.
```
**Example 3:**
```
Input: n = 4, requests = [[0,3],[3,1],[1,2],[2,0]]
Output: 4
```
**Constraints**:
* 2 <= `cookies.length` <= 8
* 1 <= `cookies[i]` <= 10^5^
* 2 <= `k` <= `cookies.length`
### 解答
### Reference
[回到題目列表](https://hackmd.io/@Marsgoat/leetcode_every_day)