require_relative 'util'

# --- Day 2: Corruption Checksum ---
#
# As you walk through the door, a glowing humanoid shape yells in your
# direction. "You there! Your state appears to be idle. Come help us
# repair the corruption in this spreadsheet - if we take another
# millisecond, we'll have to display an hourglass cursor!"
#
# The spreadsheet consists of rows of apparently-random numbers. To
# make sure the recovery process is on the right track, they need you
# to calculate the spreadsheet's checksum. For each row, determine the
# difference between the largest value and the smallest value; the
# checksum is the sum of all of these differences.
#
# For example, given the following spreadsheet:
#
# 5 1 9 5
# 7 5 3
# 2 4 6 8
#
# - The first row's largest and smallest values are 9 and 1, and their
#   difference is 8.
# - The second row's largest and smallest values are 7 and 3, and
#   their difference is 4.
# - The third row's difference is 6.
#
# In this example, the spreadsheet's checksum would be 8 + 4 + 6 = 18.
#
# What is the checksum for the spreadsheet in your puzzle input?

input = File.open('02.txt') do |f|
  f.readlines.map { |row| row.split.map(&:to_i) }
end

def easy(rows)
  rows.map { |row| row.max - row.min }.sum
end

test_input = [[5, 1, 9, 5], [7, 5, 3], [2, 4, 6, 8]]
assert(easy(test_input) == 18)
puts "easy(input): #{easy(input)}"

# --- Part Two ---
#
# "Great work; looks like we're on the right track after all. Here's a
# star for your effort." However, the program seems a little
# worried. Can programs be worried?
#
# "Based on what we're seeing, it looks like all the User wanted is
# some information about the evenly divisible values in the
# spreadsheet. Unfortunately, none of us are equipped for that kind of
# calculation - most of us specialize in bitwise operations."
#
# It sounds like the goal is to find the only two numbers in each row
# where one evenly divides the other - that is, where the result of
# the division operation is a whole number. They would like you to
# find those numbers on each line, divide them, and add up each line's
# result.
#
# For example, given the following spreadsheet:
#
# 5 9 2 8
# 9 4 7 3
# 3 8 6 5
#
# - In the first row, the only two numbers that evenly divide are 8
#   and 2; the result of this division is 4.
# - In the second row, the two numbers are 9 and 3; the result is 3.
# - In the third row, the result is 2.
#
# In this example, the sum of the results would be 4 + 3 + 2 = 9.
#
# What is the sum of each row's result in your puzzle input?

def divides?(a, b)
  if a < b && (b % a).zero?
    b / a
  elsif a > b && (a % b).zero?
    a / b
  elsif a == b
    a
  else
    0
  end
end

def hard(rows)
  rows.map { |row| row.combination(2).map { |a, b| divides?(a, b) }.sum }.sum
end

test_input = [[5, 9, 2, 8], [9, 4, 7, 3], [3, 8, 6, 5]]
assert(hard(test_input) == 9)
puts "hard(input): #{hard(input)}"