0881-boats-to-save-people.rb

# frozen_string_literal: true

# 881. Boats to Save People
# https://leetcode.com/problems/boats-to-save-people

=begin

You are given an array people where people[i] is the weight of the ith person, and an infinite number of boats where each boat can carry a maximum weight of limit. Each boat carries at most two people at the same time, provided the sum of the weight of those people is at most limit.

Return the minimum number of boats to carry every given person.

### Example 1:
Input: people = [1,2], limit = 3
Output: 1
Explanation: 1 boat (1, 2)

### Example 2:
Input: people = [3,2,2,1], limit = 3
Output: 3
Explanation: 3 boats (1, 2), (2) and (3)

### Example 3:
Input: people = [3,5,3,4], limit = 5
Output: 4
Explanation: 4 boats (3), (3), (4), (5)

### Constraints:
* 1 <= people.length <= 5 * 104
* 1 <= people[i] <= limit <= 3 * 104

=end

# @param {Integer[]} people
# @param {Integer} limit
# @return {Integer}
def num_rescue_boats(people, limit)
  people.sort!

  left = 0
  right = people.count - 1
  boat_count = 0

  loop do
    left += 1 if people[left] + people[right] <= limit
    boat_count += 1
    break if left >= right
    right -= 1
  end

  boat_count
end

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

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