1887-reduction-operations-to-make-the-array-elements-equal.rb

# frozen_string_literal: true

# 1887. Reduction Operations to Make the Array Elements Equal
# Medium
# https://leetcode.com/problems/reduction-operations-to-make-the-array-elements-equal

=begin
Given an integer array nums, your goal is to make all elements in nums equal. To complete one operation, follow these steps:
1. Find the largest value in nums. Let its index be i (0-indexed) and its value be largest. If there are multiple elements with the largest value, pick the smallest i.
2. Find the next largest value in nums strictly smaller than largest. Let its value be nextLargest.
3. Reduce nums[i] to nextLargest.
Return the number of operations to make all elements in nums equal.

Example 1:
Input: nums = [5,1,3]
Output: 3
Explanation: It takes 3 operations to make all elements in nums equal:
1. largest = 5 at index 0. nextLargest = 3. Reduce nums[0] to 3. nums = [3,1,3].
2. largest = 3 at index 0. nextLargest = 1. Reduce nums[0] to 1. nums = [1,1,3].
3. largest = 3 at index 2. nextLargest = 1. Reduce nums[2] to 1. nums = [1,1,1].

Example 2:
Input: nums = [1,1,1]
Output: 0
Explanation: All elements in nums are already equal.

Example 3:
Input: nums = [1,1,2,2,3]
Output: 4
Explanation: It takes 4 operations to make all elements in nums equal:
1. largest = 3 at index 4. nextLargest = 2. Reduce nums[4] to 2. nums = [1,1,2,2,2].
2. largest = 2 at index 2. nextLargest = 1. Reduce nums[2] to 1. nums = [1,1,1,2,2].
3. largest = 2 at index 3. nextLargest = 1. Reduce nums[3] to 1. nums = [1,1,1,1,2].
4. largest = 2 at index 4. nextLargest = 1. Reduce nums[4] to 1. nums = [1,1,1,1,1].

Constraints:
1 <= nums.length <= 5 * 104
1 <= nums[i] <= 5 * 104
=end

# @param {Integer[]} nums
# @return {Integer}
def reduction_operations(nums)
  nums.sort!

  n = nums.size
  prev = nums[0]
  current_op = 0
  total = 0

  1.upto(n - 1) do |i|
    current = nums[i]
    if current > prev
      current_op += 1
      prev = current
    end

    total += current_op
  end

  total
end

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

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