Initial commit for day 1

Gemfile

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+ruby '~> 3.0'
+source "https://rubygems.org"

Gemfile.lock

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+GEM
+  remote: https://rubygems.org/
+  specs:
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+
+RUBY VERSION
+   ruby 3.0.2p107
+
+BUNDLED WITH
+   2.1.4

gemset.nix

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+{
+}

nixpkgs.nix

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+let
+  channel-ref = "nixos-21.05";
+in
+  import (fetchTarball {
+    url = "https://github.com/NixOS/nixpkgs/archive/${channel-ref}.tar.gz";
+  }) {}

ruby-version.nix

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+with (import ./nixpkgs.nix);
+pkgs.ruby_3_0

shell.nix

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+with (import ./nixpkgs.nix);
+let
+  ruby_version = import ./ruby-version.nix;
+  gems = bundlerEnv {
+    name = "advent-of-code";
+    ruby = ruby_version;
+    gemdir = ./.;
+  };
+in stdenv.mkDerivation {
+  name = "qa-mds";
+  buildInputs = [ gems gems.wrappedRuby ];
+  shellHook = ''
+      if ! [ $NO_CHANGE_PROMPT ]; then
+        export PS1='\[\033[1;31m\]λ\[\033[0m\] '
+        export PS2='\[\033[1;31m\]|\[\033[0m\] '
+      fi
+  '';
+}

src/day1/day1.rb

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+inputs = ARGF.read.lines
+
+begin 
+  inputs.map! {|input| Integer(input)}
+rescue ArgumentError
+  puts "An input item wasn't a number, invalid input"
+end
+
+larger_than_before = 0
+before = nil
+inputs.each do |input|
+  before = input if before.nil?
+  larger_than_before += 1 if input > before
+  before = input
+end
+
+puts "Amount of measurements larger than before: #{larger_than_before}"
+
+larger_than_previous_window = 0
+previous_window = nil
+window = []
+inputs.each_with_index do |input, index|
+  unless index+2 >= inputs.size # Handle the last window not overreaching
+    window = [inputs[index], inputs[index+1], inputs[index+2]]
+    if previous_window && window.reduce(:+) > previous_window.reduce(:+) 
+      larger_than_previous_window += 1
+    end
+    previous_window = window
+  end
+end
+
+puts "Amount of measurements larger than preivous window: #{larger_than_previous_window}"