2601-prime-subtraction-operation.rb

# frozen_string_literal: true

# 2601. Prime Subtraction Operation
# https://leetcode.com/problems/prime-subtraction-operation
# Medium

=begin
You are given a 0-indexed integer array nums of length n.
You can perform the following operation as many times as you want:
* Pick an index i that you haven’t picked before, and pick a prime p strictly less than nums[i], then subtract p from nums[i].
Return true if you can make nums a strictly increasing array using the above operation and false otherwise.
A strictly increasing array is an array whose each element is strictly greater than its preceding element.

Example 1:
Input: nums = [4,9,6,10]
Output: true
Explanation: In the first operation: Pick i = 0 and p = 3, and then subtract 3 from nums[0], so that nums becomes [1,9,6,10].
In the second operation: i = 1, p = 7, subtract 7 from nums[1], so nums becomes equal to [1,2,6,10].
After the second operation, nums is sorted in strictly increasing order, so the answer is true.
Example 2:
Input: nums = [6,8,11,12]
Output: true
Explanation: Initially nums is sorted in strictly increasing order, so we don't need to make any operations.
Example 3:
Input: nums = [5,8,3]
Output: false
Explanation: It can be proven that there is no way to perform operations to make nums sorted in strictly increasing order, so the answer is false.

Constraints:
* 1 <= nums.length <= 1000
* 1 <= nums[i] <= 1000
* nums.length == n
=end

# @param {Integer[]} nums
# @return {Boolean}
def prime_sub_operation(nums)
  primes = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503, 509, 521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593, 599, 601, 607, 613, 617, 619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691, 701, 709, 719, 727, 733, 739, 743, 751, 757, 761, 769, 773, 787, 797, 809, 811, 821, 823, 827, 829, 839, 853, 857, 859, 863, 877, 881, 883, 887, 907, 911, 919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991, 997, 1009, 1013, 1019, 1021]

  curr_value = 1
  i = 0

  while i < nums.length
    difference = nums[i] - curr_value

    return false if difference < 0

    if difference == 0 || primes.include?(difference)
      i += 1
      curr_value += 1
    else
      curr_value += 1
    end
  end

  true
end

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

require "test/unit"
class Test_prime_sub_operation < Test::Unit::TestCase
  def test_
    assert_equal true, prime_sub_operation([4, 9, 6, 10])
    assert_equal true, prime_sub_operation([6, 8, 11, 12])
    assert_equal false, prime_sub_operation([5, 8, 3])
  end
end