1561-maximum-number-of-coins-you-can-get.rb

# frozen_string_literal: true

# 1561. Maximum Number of Coins You Can Get
# Medium
# https://leetcode.com/problems/maximum-number-of-coins-you-can-get

=begin
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 ith 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:
3 <= piles.length <= 105
piles.length % 3 == 0
1 <= piles[i] <= 104
=end

# @param {Integer[]} piles
# @return {Integer}
def max_coins(piles)
  piles.sort!

  j = 0
  i = piles.length - 2
  sum = 0

  while i > j do
    sum += piles[i]
    i -= 2
    j += 1
  end

  sum
end

# **************** #
#       TEST       #
# **************** #

require "test/unit"
class Test_max_coins < Test::Unit::TestCase
  def test_
    assert_equal 9, max_coins([2, 4, 1, 2, 7, 8])
    assert_equal 4, max_coins([2, 4, 5])
    assert_equal 18, max_coins([9, 8, 7, 6, 5, 1, 2, 3, 4])
  end
end