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# 1561. Maximum Number of Coins You Can Get

<https://leetcode.com/problems/maximum-number-of-coins-you-can-get>

## Description

There are 3n piles of coins of varying size, you and your friends will take piles of coins as follows:

* In each step, you will choose **any**3 piles of coins (not necessarily consecutive).
* Of your choice, Alice will pick the pile with the maximum number of coins.
* You will pick the next pile with maximum number of coins.
* Your friend Bob will pick the last pile.
* Repeat until there are no more piles of coins.

Given an array of integers `piles` where `piles[i]` is the number of coins in the `ith` pile.

Return the maximum number of coins which you can have.

**Example 1:**

```
**Input:** piles = [2,4,1,2,7,8]
**Output:** 9
**Explanation:** Choose the triplet (2, 7, 8), Alice Pick the pile with 8 coins, you the pile with **7** coins and Bob the last one.
Choose the triplet (1, 2, 4), Alice Pick the pile with 4 coins, you the pile with **2** coins and Bob the last one.
The maximum number of coins which you can have are: 7 + 2 = 9.
On the other hand if we choose this arrangement (1, **2**, 8), (2, **4**, 7) you only get 2 + 4 = 6 coins which is not optimal.
```

**Example 2:**

```
**Input:** piles = [2,4,5]
**Output:** 4
```

**Example 3:**

```
**Input:** piles = [9,8,7,6,5,1,2,3,4]
**Output:** 18
```

**Constraints:**

* `3 <= piles.length <= 10^5`
* `piles.length % 3 == 0`
* `1 <= piles[i] <= 10^4`

## ac

```java
```