2366-minimum-replacements-to-sort-the-array.rb

# frozen_string_literal: true

# 2366. Minimum Replacements to Sort the Array
# Hard
# https://leetcode.com/problems/minimum-replacements-to-sort-the-array

=begin
You are given a 0-indexed integer array nums. In one operation you can replace any element of the array with any two elements that sum to it.
For example, consider nums = [5,6,7]. In one operation, we can replace nums[1] with 2 and 4 and convert nums to [5,2,4,7].
Return the minimum number of operations to make an array that is sorted in non-decreasing order.

Example 1:
Input: nums = [3,9,3]
Output: 2
Explanation: Here are the steps to sort the array in non-decreasing order:
- From [3,9,3], replace the 9 with 3 and 6 so the array becomes [3,3,6,3]
- From [3,3,6,3], replace the 6 with 3 and 3 so the array becomes [3,3,3,3,3]
There are 2 steps to sort the array in non-decreasing order. Therefore, we return 2.

Example 2:
Input: nums = [1,2,3,4,5]
Output: 0
Explanation: The array is already in non-decreasing order. Therefore, we return 0.

Constraints:
* 1 <= nums.length <= 10^5
* 1 <= nums[i] <= 109
=end

# @param {Integer[]} nums
# @return {Integer}
def minimum_replacement(nums)
  result = 0
  n = nums.size

  (n - 2).downto(0) do |i|
    curr = nums[i]
    _next = nums[i + 1]

    if curr > _next
      higher_bound = (curr / _next.to_f).ceil
      result += higher_bound - 1
      nums[i] = (curr / higher_bound).floor
    end
  end

  result
end

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

require "test/unit"
class Test_minimum_replacement < Test::Unit::TestCase
  def test_
    assert_equal 2, minimum_replacement([3, 9, 3])
    assert_equal 0, minimum_replacement([1, 2, 3, 4, 5])
  end
end