1508-range-sum-of-sorted-subarray-sums.rb

# frozen_string_literal: true

# 1508. Range Sum of Sorted Subarray Sums
# Medium
# https://leetcode.com/problems/range-sum-of-sorted-subarray-sums

=begin
You are given the array nums consisting of n positive integers. You computed the sum of all non-empty continuous subarrays from the array and then sorted them in non-decreasing order, creating a new array of n * (n + 1) / 2 numbers.
Return the sum of the numbers from index left to index right (indexed from 1), inclusive, in the new array. Since the answer can be a huge number return it modulo 109 + 7.

Example 1:
Input: nums = [1,2,3,4], n = 4, left = 1, right = 5
Output: 13
Explanation: All subarray sums are 1, 3, 6, 10, 2, 5, 9, 3, 7, 4. After sorting them in non-decreasing order we have the new array [1, 2, 3, 3, 4, 5, 6, 7, 9, 10]. The sum of the numbers from index le = 1 to ri = 5 is 1 + 2 + 3 + 3 + 4 = 13.

Example 2:
Input: nums = [1,2,3,4], n = 4, left = 3, right = 4
Output: 6
Explanation: The given array is the same as example 1. We have the new array [1, 2, 3, 3, 4, 5, 6, 7, 9, 10]. The sum of the numbers from index le = 3 to ri = 4 is 3 + 3 = 6.

Example 3:
Input: nums = [1,2,3,4], n = 4, left = 1, right = 10
Output: 50

Constraints:
* n == nums.length
* 1 <= nums.length <= 1000
* 1 <= nums[i] <= 100
* 1 <= left <= right <= n * (n + 1) / 2
=end

# @param {Integer[]} nums
# @param {Integer} n
# @param {Integer} left
# @param {Integer} right
# @return {Integer}
MOD = 10**9 + 7

def range_sum(nums, n, left, right)
  nums
    .each_with_index.each_with_object([0]) do |(v, idx), res|
      res << (sum = res[-idx] + v)
      nums.first(idx).each { |w| res << (sum -= w) }
    end
    .drop(1).sort[left - 1..right - 1].sum % MOD
end

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

require "test/unit"
class Test_range_sum < Test::Unit::TestCase
  def test_
    assert_equal 13, range_sum([1, 2, 3, 4], 4, 1, 5)
    assert_equal 6, range_sum([1, 2, 3, 4], 4, 3, 4)
    assert_equal 50, range_sum([1, 2, 3, 4], 4, 1, 10)
  end
end