1652-defuse-the-bomb.rb

# frozen_string_literal: true

# 1652. Defuse the Bomb
# https://leetcode.com/problems/defuse-the-bomb
# Easy

=begin
You have a bomb to defuse, and your time is running out! Your informer will provide you with a circular array code of length of n and a key k.
To decrypt the code, you must replace every number. All the numbers are replaced simultaneously.
* If k > 0, replace the ith number with the sum of the next k numbers.
* If k < 0, replace the ith number with the sum of the previous k numbers.
* If k == 0, replace the ith number with 0.
As code is circular, the next element of code[n-1] is code[0], and the previous element of code[0] is code[n-1].
Given the circular array code and an integer key k, return the decrypted code to defuse the bomb!

Example 1:
Input: code = [5,7,1,4], k = 3
Output: [12,10,16,13]
Explanation: Each number is replaced by the sum of the next 3 numbers. The decrypted code is [7+1+4, 1+4+5, 4+5+7, 5+7+1]. Notice that the numbers wrap around.
Example 2:
Input: code = [1,2,3,4], k = 0
Output: [0,0,0,0]
Explanation: When k is zero, the numbers are replaced by 0.
Example 3:
Input: code = [2,4,9,3], k = -2
Output: [12,5,6,13]
Explanation: The decrypted code is [3+9, 2+3, 4+2, 9+4]. Notice that the numbers wrap around again. If k is negative, the sum is of the previous numbers.

Constraints:
* n == code.length
* 1 <= n <= 100
* 1 <= code[i] <= 100
* -(n - 1) <= k <= n - 1
=end

# @param {Integer[]} code
# @param {Integer} k
# @return {Integer[]}
def decrypt(circ, k)
  n = circ.size
  result = Array.new(n, 0)

  return result if k == 0

  w_sum = 0
  start = k > 0 ? 1 : n + k
  end_pos = k > 0 ? k : n - 1

  (start..end_pos).each do |i|
    w_sum += circ[i % n]
  end

  n.times do |i|
    result[i] = w_sum
    w_sum -= circ[(start + i) % n]
    w_sum += circ[(end_pos + i + 1) % n]
  end

  result
end

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

require "test/unit"

class Test_decrypt < Test::Unit::TestCase
  def test_
    assert_equal [12, 10, 16, 13], decrypt([5, 7, 1, 4], 3)
    assert_equal [0, 0, 0, 0], decrypt([1, 2, 3, 4], 0)
    assert_equal [12, 5, 6, 13], decrypt([2, 4, 9, 3], -2)
  end
end