1561. Maximum Number of Coins You Can Get (#165)

Author: remy727

README.md

@@ -367,6 +367,7 @@
 | 1539 | Kth Missing Positive Number | [Ruby](./algorithms/ruby/1539-kth-missing-positive-number.rb) | Easy |
 | 1547 | Minimum Cost to Cut a Stick | [Ruby](./algorithms/ruby/1547-minimum-cost-to-cut-a-stick.rb) | Hard |
 | 1557 | Minimum Number of Vertices to Reach All Nodes | [Ruby](./algorithms/ruby/1557-minimum-number-of-vertices-to-reach-all-nodes.rb) | Medium |
+| 1561 | Maximum Number of Coins You Can Get | [Ruby](./algorithms/ruby/1561-maximum-number-of-coins-you-can-get.rb) | Medium |
 | 1569 | Number of Ways to Reorder Array to Get Same BST | [Ruby](./algorithms/ruby/1569-number-of-ways-to-reorder-array-to-get-same-bst.rb) | Hard |
 | 1572 | Matrix Diagonal Sum | [Ruby](./algorithms/ruby/1572-matrix-diagonal-sum.rb) | Easy |
 | 1575 | Count All Possible Routes | [Ruby](./algorithms/ruby/1575-count-all-possible-routes.rb) | Hard |

algorithms/ruby/1561-maximum-number-of-coins-you-can-get.rb

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+# 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