day 13 part 1

examples/13.txt

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+#.##..##.
+..#.##.#.
+##......#
+##......#
+..#.##.#.
+..##..##.
+#.#.##.#.
+
+#...##..#
+#....#..#
+..##..###
+#####.##.
+#####.##.
+..##..###
+#....#..#

lib/days/13.rb

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+class Day13
+
+  def part1(input)
+    cols = 0
+    rows = 0
+
+    input.split("\n\n").each do |chunk|
+      mirror_column = find_mirror_column(chunk)
+
+      if mirror_column
+        cols += mirror_column + 1
+      else
+        mirror_row = find_mirror_row(chunk)
+        rows += mirror_row + 1
+      end
+    end
+
+    (rows * 100) + cols
+  end
+
+  def find_mirror_column(chunk)
+    rows = chunk.split("\n")
+
+    mirror_column = nil
+
+    (0..(rows.first.length - 2)).each do |n|
+      is_mirror = true
+
+      (0..(rows.length - 1)).each do |i|
+        row = rows[i]
+
+        left = row[0..n]
+        right = row[(n + 1), left.length]
+
+        if left.length > right.length
+          left = left[(left.length - right.length)..]
+        end
+
+        if left != right.reverse
+          is_mirror = false
+          break
+        end
+      end
+
+      if is_mirror
+        mirror_column = n
+        break
+      end
+    end
+
+    mirror_column
+  end
+
+  def find_mirror_row(chunk)
+    rows = chunk.split("\n")
+
+    mirror_row = nil
+
+    (0..(rows.length - 2)).each do |n|
+      is_mirror = true
+
+      (0..(rows[n].length - 1)).each do |i|
+        column = rows.map { |r| r[i] }.join
+
+        top = column[0..n]
+        bottom = column[(n + 1), top.length]
+
+        if top.length > bottom.length
+          top = top[(top.length - bottom.length)..]
+        end
+
+        if top != bottom.reverse
+          is_mirror = false
+          break
+        end
+      end
+
+      if is_mirror
+        mirror_row = n
+        break
+      end
+    end
+
+    mirror_row
+  end
+
+  def part2(input)
+    'TODO'
+  end
+
+end

test/13_test.rb

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+require 'minitest/autorun'
+require 'minitest/pride'
+require_relative '../app'
+
+class TestDay13 < Minitest::Test
+  def setup
+    @data = File.read(File.join(APP_ROOT, 'examples', '13.txt')).rstrip
+    @day = Day13.new
+  end
+
+  def test_part1
+    assert_equal @day.part1(@data), 405
+  end
+
+  def test_part2
+    assert_equal @day.part2(@data), ''
+  end
+end