1716-calculate-money-in-leetcode-bank.rb

# frozen_string_literal: true

# 1716. Calculate Money in Leetcode Bank
# Easy
# https://leetcode.com/problems/calculate-money-in-leetcode-bank

=begin
Hercy wants to save money for his first car. He puts money in the Leetcode bank every day.
He starts by putting in $1 on Monday, the first day. Every day from Tuesday to Sunday, he will put in $1 more than the day before. On every subsequent Monday, he will put in $1 more than the previous Monday.
Given n, return the total amount of money he will have in the Leetcode bank at the end of the nth day.

Example 1:
Input: n = 4
Output: 10
Explanation: After the 4th day, the total is 1 + 2 + 3 + 4 = 10.

Example 2:
Input: n = 10
Output: 37
Explanation: After the 10th day, the total is (1 + 2 + 3 + 4 + 5 + 6 + 7) + (2 + 3 + 4) = 37. Notice that on the 2nd Monday, Hercy only puts in $2.

Example 3:
Input: n = 20
Output: 96
Explanation: After the 20th day, the total is (1 + 2 + 3 + 4 + 5 + 6 + 7) + (2 + 3 + 4 + 5 + 6 + 7 + 8) + (3 + 4 + 5 + 6 + 7 + 8) = 96.

Constraints:
1 <= n <= 1000
=end

# @param {Integer} n
# @return {Integer}
def total_money(n)
  k, x = n / 7, n % 7
  (7 * k * (k + 7) / 2) + (x * (2 * k + x + 1) / 2)
end

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

require "test/unit"
class Test_total_money < Test::Unit::TestCase
  def test_
    assert_equal 10, total_money(4)
    assert_equal 37, total_money(10)
    assert_equal 96, total_money(20)
  end
end