1140-stone-game-ii.rb

# frozen_string_literal: true

# 1140. Stone Game II
# https://leetcode.com/problems/stone-game-ii/
# Medium

=begin
Alice and Bob continue their games with piles of stones. There are a number of piles arranged in a row, and each pile has a positive integer number of stones piles[i]. The objective of the game is to end with the most stones.

Alice and Bob take turns, with Alice starting first. Initially, M = 1.

On each player's turn, that player can take all the stones in the first X remaining piles, where 1 <= X <= 2M. Then, we set M = max(M, X).

The game continues until all the stones have been taken.

Assuming Alice and Bob play optimally, return the maximum number of stones Alice can get.

Example 1:
Input: piles = [2,7,9,4,4]
Output: 10
Explanation: If Alice takes one pile at the beginning, Bob takes two piles, then Alice takes 2 piles again. Alice can get 2 + 4 + 4 = 10 piles in total. If Alice takes two piles at the beginning, then Bob can take all three piles left. In this case, Alice get 2 + 7 = 9 piles in total. So we return 10 since it's larger.

Example 2:
Input: piles = [1,2,3,4,5,100]
Output: 104

Constraints:
1 <= piles.length <= 100
1 <= piles[i] <= 104
=end

# @param {Integer[]} piles
# @return {Integer}
defmin(a,b)
a < b ? a : b
end

defmax(a,b)
a > b ? a : b
end

defstone_game_ii(piles)
ps=piles.reduce([0]){ |arr,num| arr << arr[-1] + num}
z=ps.size
game=Array.new(z)do |i|
remaining_stones=ps[-1] - ps[i]
Hash.newdo |h,m|
min_best_response=(i + 1..min(i + 2 * m,z)).map{game[_1][max(m,_1 - i)]}.min
h[m]=remaining_stones - min_best_response
end
end << ->_{0}

game[0][1]
end

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

require"test/unit"
classTest_stone_game_ii < Test::Unit::TestCase
deftest_
assert_equal10,stone_game_ii([2,7,9,4,4])
assert_equal104,stone_game_ii([1,2,3,4,5,100])
end
end