From d2493389b8111b581c75933a1609c4df541f3836 Mon Sep 17 00:00:00 2001
From: Greg Woods <greg.woods@moserit.com>
Date: Sun, 17 Dec 2023 01:04:49 -0500
Subject: [PATCH] Day 14 part 2

---
 lib/days/14.rb  | 87 ++++++++++++++++++++++++++++++++++++++-----------
 test/14_test.rb |  2 +-
 2 files changed, 69 insertions(+), 20 deletions(-)

diff --git a/lib/days/14.rb b/lib/days/14.rb
index e417285..c2667d5 100644
--- a/lib/days/14.rb
+++ b/lib/days/14.rb
@@ -1,28 +1,26 @@
 class Day14
 
-  def part1(input)
+  def parse(input)
     lines = input.split("\n")
 
-    columns = []
+    grid = []
 
     lines.length.times do |n|
       lines[n].chars.each_with_index do |char, i|
-        columns[i] ||= []
-        columns[i] << char
+        grid[i] ||= []
+        grid[i] << char
       end
     end
 
-    columns = columns.map do |c|
-      shift_column(c)
-    end
+    grid
+  end
 
+  def calculate(grid)
     value = 0
 
-    columns.each do |col|
+    grid.each do |col|
       col.each_with_index do |obj, index|
-        if obj == 'O'
-          value += (col.length - index)
-        end
+        value += (col.length - index) if obj == 'O'
       end
     end
 
@@ -30,34 +28,85 @@ def part1(input)
   end
 
   def shift_column(column)
+    new_column = column
+
     column.length.times do |n|
       next if n.zero?
 
       n.times do |i|
         position = n - i
 
-        char = column[position]
-        prev_char = column[position - 1]
+        char = new_column[position]
+        prev_char = new_column[position - 1]
 
         if char == 'O' && prev_char == '.'
-          column[position] = '.'
-          column[position - 1] = 'O'
+          new_column[position] = '.'
+          new_column[position - 1] = 'O'
         else
           break
         end
       end
     end
 
-    column
+    new_column
+  end
+
+  def shift_grid(grid)
+    grid.map do |column|
+      shift_column(column)
+    end
+  end
+
+  def rotate_clockwise(grid)
+    new_grid = []
+
+    grid.each do |column|
+      column.reverse.each_with_index do |item, index|
+        new_grid[index] ||= []
+        new_grid[index] << item
+      end
+    end
+
+    new_grid
   end
 
-  def rotate_clockwise(columns)
-    new_columns = []
+  def print_grid(grid)
+    grid.first.length.times do |y|
+      grid.length.times do |x|
+        print grid[x][y]
+      end
+      print "\n"
+    end
+  end
 
+  def part1(input)
+    calculate(shift_grid(parse(input)))
   end
 
   def part2(input)
-    'TODO'
+    grid = parse(input)
+
+    history = [grid.dup]
+
+    iterations = 1_000_000_000
+
+    iterations.times do |i|
+      4.times do
+        grid = rotate_clockwise(shift_grid(grid))
+      end
+
+      if history.include?(grid)
+        loop_start_idx = history.index(grid)
+        the_loop = history[loop_start_idx..]
+        idx = ((iterations - i) % the_loop.length) - 1
+
+        return calculate(the_loop[idx])
+      end
+
+      history << grid.map(&:dup)
+    end
+
+    raise 'Should not get this far!'
   end
 
 end
diff --git a/test/14_test.rb b/test/14_test.rb
index d0d4d82..32064fd 100644
--- a/test/14_test.rb
+++ b/test/14_test.rb
@@ -13,6 +13,6 @@ def test_part1
   end
 
   def test_part2
-    assert_equal @day.part2(@data), ''
+    assert_equal @day.part2(@data), 64
   end
 end