Day 4 Ruby solutions

Author: creideiki

04-1.rb

@@ -0,0 +1,37 @@
+#!/usr/bin/env ruby
+
+$haystack = File.read('04.input').lines.map(&:strip).map(&:chars)
+
+def find_dir(needle, x, y, dx, dy)
+  return true if needle.empty?
+  return false if x < 0 or
+                  x >= $haystack[0].size or
+                  y < 0 or
+                  y >= $haystack.size
+  return false unless $haystack[y][x] == needle[0]
+
+  find_dir(needle[1..], x + dx, y + dy, dx, dy)
+end
+
+def find(x, y)
+  needle = 'XMAS'
+
+  count = 0
+  [-1, 0, 1].each do |dx|
+    [-1, 0, 1].each do |dy|
+      next if dx.zero? and dy.zero?
+
+      count += 1 if find_dir(needle, x, y, dx, dy)
+    end
+  end
+  count
+end
+
+count = 0
+$haystack.each_index do |y|
+  $haystack[0].each_index do |x|
+    count += find(x, y)
+  end
+end
+
+puts count

04-2.rb

@@ -0,0 +1,59 @@
+#!/usr/bin/env ruby
+
+require 'numo/narray'
+
+class Puzzle
+  def initialize(input)
+    @height = input.size
+    @width = input[0].size
+    @map = Numo::UInt8.zeros(@height, @width)
+    @height.times do |y|
+      @width.times do |x|
+        @map[y, x] = input[y][x].codepoints[0]
+      end
+    end
+
+    mas = [
+      'M.S'.codepoints,
+      '.A.'.codepoints,
+      'M.S'.codepoints
+    ]
+    @mas_height = mas.size
+    @mas_width = mas[0].size
+    xmas = Numo::UInt8.zeros(3, 3)
+    @mas_height.times do |y|
+      @mas_width.times do |x|
+        xmas[y, x] = mas[y][x]
+      end
+    end
+    @xmases = [xmas, xmas.rot90(1), xmas.rot90(2), xmas.rot90(3)]
+  end
+
+  def match?(y, x)
+    @xmases.any? do |xmas|
+      res = true
+      @mas_height.times do |my|
+        @mas_width.times do |mx|
+          next if xmas[my, mx] == 46 # .
+
+          res = false if xmas[my, mx] != @map[y + my, x + mx]
+        end
+      end
+      res
+    end
+  end
+
+  def count_matches
+    count = 0
+    (@height - @mas_height + 1).times do |y|
+      (@width - @mas_width + 1).times do |x|
+        count += 1 if match?(y, x)
+      end
+    end
+    count
+  end
+end
+
+input = File.read('04.input').lines.map(&:strip)
+puzzle = Puzzle.new(input)
+puts puzzle.count_matches