Ruby 3.0의 출시 - 1일차 - 복구 보고

#!/bin/bash

# Ha, here we are using Bash.

# Find something which starts with the number. I name the actual
# scripts decently, this not so much
matching=`find . -type f -name "$1_*.rb" | head -n 1`

# Then peel the extension off of it
name=`basename $matching .rb`

# ...and throw it to Ruby, with the input from the inputs dir with the same
# name, except a txt extension
ruby ./"$name".rb ./inputs/"$name".txt

TARGET = 2020

n = 1500

duals = {}
duals[TARGET - n] = n
# => { 520 => 1500 }

n = 520
duals[n]
# => 1500

# Give a name to the idea of not finding a number,
# but make it compatible with the output functions
# to not crash on error
NOT_FOUND = [-1, -1]

def duals(input, target: 2020)
  # Transform our input into ints, and bring along a hash for the ride
  input.map(&:to_i).each_with_object({}) do |v, duals|
    # If we find a dual number, return it and `v`, we have
    # our answer
    return [v, duals[v]] if duals[v]

    # Otherwise set the target so we can find it next
    # time around
    duals[target - v] = v
  end

  # Otherwise we return back our idea of "not found"
  NOT_FOUND
end

def dual_product(input) = duals(input).reduce(1, :*)

Why the 1 with reduce? Well if we have an empty array we want a sane return value. For addition that value is 0 as you can add any number to it and get back that same number. Same idea with 1 and multiplication here.

Granted this concept has a name, identity or empty, but that's the subject of another post.

def product_duals(...) = duals(...).reduce(1, :*)

def product_duals(input) = duals(...).reduce(1, :*)
# SyntaxError ((irb):22: unexpected ...)

File.readlines(ARGV[0]).then { puts product_duals(_1) }

1.tap { |v| v + 1 }
# => 1

1.then { |v| v + 1 }
# => 2

then { puts product_duals(_1) }