1894-find-the-student-that-will-replace-the-chalk.rb

# frozen_string_literal: true

# 1894. Find the Student that Will Replace the Chalk
# Medium
# https://leetcode.com/problems/find-the-student-that-will-replace-the-chalk

=begin
There are n students in a class numbered from 0 to n - 1. The teacher will give each student a problem starting with the student number 0, then the student number 1, and so on until the teacher reaches the student number n - 1. After that, the teacher will restart the process, starting with the student number 0 again.
You are given a 0-indexed integer array chalk and an integer k. There are initially k pieces of chalk. When the student number i is given a problem to solve, they will use chalk[i] pieces of chalk to solve that problem. However, if the current number of chalk pieces is strictly less than chalk[i], then the student number i will be asked to replace the chalk.
Return the index of the student that will replace the chalk pieces.

Example 1:
Input: chalk = [5,1,5], k = 22
Output: 0
Explanation: The students go in turns as follows:
- Student number 0 uses 5 chalk, so k = 17.
- Student number 1 uses 1 chalk, so k = 16.
- Student number 2 uses 5 chalk, so k = 11.
- Student number 0 uses 5 chalk, so k = 6.
- Student number 1 uses 1 chalk, so k = 5.
- Student number 2 uses 5 chalk, so k = 0.
Student number 0 does not have enough chalk, so they will have to replace it.
Example 2:

Input: chalk = [3,4,1,2], k = 25
Output: 1
Explanation: The students go in turns as follows:
- Student number 0 uses 3 chalk so k = 22.
- Student number 1 uses 4 chalk so k = 18.
- Student number 2 uses 1 chalk so k = 17.
- Student number 3 uses 2 chalk so k = 15.
- Student number 0 uses 3 chalk so k = 12.
- Student number 1 uses 4 chalk so k = 8.
- Student number 2 uses 1 chalk so k = 7.
- Student number 3 uses 2 chalk so k = 5.
- Student number 0 uses 3 chalk so k = 2.
Student number 1 does not have enough chalk, so they will have to replace it.

Constraints:
* chalk.length == n
* 1 <= n <= 105
* 1 <= chalk[i] <= 105
* 1 <= k <= 109
=end

# @param {Integer[]} chalk
# @param {Integer} k
# @return {Integer}
def chalk_replacer(chalk, k)
  k %= chalk.sum
  chalk.each_with_index do |amount, i|
    k -= amount
    return i if k < 0
  end
  0
end

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

require "test/unit"
class Test_chalk_replacer < Test::Unit::TestCase
  def test_
    assert_equal 0, chalk_replacer([5, 1, 5], 22)
    assert_equal 1, chalk_replacer([3, 4, 1, 2], 25)
  end
end