1498-number-of-subsequences-that-satisfy-the-given-sum-condition.rb

# frozen_string_literal: true

# 1498. Number of Subsequences That Satisfy the Given Sum Condition
# https://leetcode.com/problems/number-of-subsequences-that-satisfy-the-given-sum-condition
# Medium

=begin
You are given an array of integers nums and an integer target.

Return the number of non-empty subsequences of nums such that the sum of the minimum and maximum element on it is less or equal to target. Since the answer may be too large, return it modulo 109 + 7.

Example 1:
Input: nums = [3,5,6,7], target = 9
Output: 4
Explanation: There are 4 subsequences that satisfy the condition.
[3] -> Min value + max value <= target (3 + 3 <= 9)
[3,5] -> (3 + 5 <= 9)
[3,5,6] -> (3 + 6 <= 9)
[3,6] -> (3 + 6 <= 9)

Example 2:
Input: nums = [3,3,6,8], target = 10
Output: 6
Explanation: There are 6 subsequences that satisfy the condition. (nums can have repeated numbers).
[3] , [3] , [3,3], [3,6] , [3,6] , [3,3,6]

Example 3:
Input: nums = [2,3,3,4,6,7], target = 12
Output: 61
Explanation: There are 63 non-empty subsequences, two of them do not satisfy the condition ([6,7], [7]).
Number of valid subsequences (63 - 2 = 61).

Constraints:
1 <= nums.length <= 105
1 <= nums[i] <= 106
1 <= target <= 106
=end

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

  result = 0

  nums.each_with_index do |num, index|
    break if (num * 2) > target

    max_index = (nums.bsearch_index { |num_searched| num_searched > (target - num) } || nums.size) - 1
    result += 2**(max_index - index)
  end

  result % (10**9 + 7)
end

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

require "test/unit"
class Test_num_subseq < Test::Unit::TestCase
  def test_
    assert_equal 4, num_subseq([3, 5, 6, 7], 9)
    assert_equal 6, num_subseq([3, 3, 6, 8], 10)
    assert_equal 61, num_subseq([2, 3, 3, 4, 6, 7], 12)
  end
end