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LC-1561

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Aug 28, 2020

LC-1561 - Maximum Number of Coins You Can Get

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 i-th pile.

Return the maximum number of coins which you can have.

  • Difficulty: MEDIUM

Examples

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

Notes

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

Solutions

  1. Sorting
    • Time complexity: O ( n log n )
    • Space complexity: O ( 1 )