2090-k-radius-subarray-averages.rb

# frozen_string_literal: true

# 2090. K Radius Subarray Averages
# Medium
# https://leetcode.com/problems/k-radius-subarray-averages

=begin
You are given a 0-indexed array nums of n integers, and an integer k.

The k-radius average for a subarray of nums centered at some index i with the radius k is the average of all elements in nums between the indices i - k and i + k (inclusive). If there are less than k elements before or after the index i, then the k-radius average is -1.

Build and return an array avgs of length n where avgs[i] is the k-radius average for the subarray centered at index i.

The average of x elements is the sum of the x elements divided by x, using integer division. The integer division truncates toward zero, which means losing its fractional part.

* For example, the average of four elements 2, 3, 1, and 5 is (2 + 3 + 1 + 5) / 4 = 11 / 4 = 2.75, which truncates to 2.

Example 1:
Input: nums = [7,4,3,9,1,8,5,2,6], k = 3
Output: [-1,-1,-1,5,4,4,-1,-1,-1]
Explanation:
- avg[0], avg[1], and avg[2] are -1 because there are less than k elements before each index.
- The sum of the subarray centered at index 3 with radius 3 is: 7 + 4 + 3 + 9 + 1 + 8 + 5 = 37.
  Using integer division, avg[3] = 37 / 7 = 5.
- For the subarray centered at index 4, avg[4] = (4 + 3 + 9 + 1 + 8 + 5 + 2) / 7 = 4.
- For the subarray centered at index 5, avg[5] = (3 + 9 + 1 + 8 + 5 + 2 + 6) / 7 = 4.
- avg[6], avg[7], and avg[8] are -1 because there are less than k elements after each index.

Example 2:
Input: nums = [100000], k = 0
Output: [100000]
Explanation:
- The sum of the subarray centered at index 0 with radius 0 is: 100000.
  avg[0] = 100000 / 1 = 100000.

Example 3:
Input: nums = [8], k = 100000
Output: [-1]
Explanation:
- avg[0] is -1 because there are less than k elements before and after index 0.

Constraints:
* n == nums.length
* 1 <= n <= 105
* 0 <= nums[i], k <= 105
=end

# @param {Integer[]} nums
# @param {Integer} k
# @return {Integer[]}
def get_averages(nums, k)
  left = 0
  curr_sum = 0
  window_size = 2 * k + 1
  result = Array.new(nums.length, -1)

  nums.each_with_index do |num, right|
    curr_sum += num

    if right - left + 1 == window_size
      avg = curr_sum / window_size
      result[right - k] = avg
      curr_sum -= nums[left]
      left += 1
    end
  end
  result
end

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

require "test/unit"
class Test_get_averages < Test::Unit::TestCase
  def test_
    assert_equal [-1, -1, -1, 5, 4, 4, -1, -1, -1], get_averages([7, 4, 3, 9, 1, 8, 5, 2, 6], 3)
    assert_equal [100000], get_averages([100000], 0)
    assert_equal [-1], get_averages([8], 100000)
  end
end