1561 - Maximum Number of Coins You Can Get.

Medium

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 the 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 <code>i^th</code> pile.

Return the maximum number of coins that 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:

• <code>3 <= piles.length <= 10⁵</code>

• piles.length % 3 == 0

• <code>1 <= pilesi<= 10⁴</code>