2742-painting-the-walls.rb

# frozen_string_literal: true

# 2742. Painting the Walls
# Hard
# https://leetcode.com/problems/painting-the-walls

=begin
You are given two 0-indexed integer arrays, cost and time, of size n representing the costs and the time taken to paint n different walls respectively. There are two painters available:

A paid painter that paints the ith wall in time[i] units of time and takes cost[i] units of money.
A free painter that paints any wall in 1 unit of time at a cost of 0. But the free painter can only be used if the paid painter is already occupied.
Return the minimum amount of money required to paint the n walls.

Example 1:
Input: cost = [1,2,3,2], time = [1,2,3,2]
Output: 3
Explanation: The walls at index 0 and 1 will be painted by the paid painter, and it will take 3 units of time; meanwhile, the free painter will paint the walls at index 2 and 3, free of cost in 2 units of time. Thus, the total cost is 1 + 2 = 3.

Example 2:
Input: cost = [2,3,4,2], time = [1,1,1,1]
Output: 4
Explanation: The walls at index 0 and 3 will be painted by the paid painter, and it will take 2 units of time; meanwhile, the free painter will paint the walls at index 1 and 2, free of cost in 2 units of time. Thus, the total cost is 2 + 2 = 4.

Constraints:
1 <= cost.length <= 500
cost.length == time.length
1 <= cost[i] <= 106
1 <= time[i] <= 500
=end

# @param {Integer[]} cost
# @param {Integer[]} time
# @return {Integer}
def paint_walls(cost, time)
  n = cost.length
  dp = Array.new(n + 1, Float::INFINITY)
  dp[0] = 0

  (0...n).each do |i|
    n.downto(1) do |j|
      dp[j] = [dp[j], dp[[j - time[i] - 1, 0].max] + cost[i]].min
    end
  end

  dp[n]
end

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

require "test/unit"
class Test_paint_walls < Test::Unit::TestCase
  def test_
    assert_equal 3, paint_walls([1, 2, 3, 2], [1, 2, 3, 2])
    assert_equal 4, paint_walls([2, 3, 4, 2], [1, 1, 1, 1])
  end
end