Days 9 to 13 2022

Author: gchan

2022/day-09/README.txt

@@ -0,0 +1,44 @@
+#!/usr/bin/env ruby
+
+require 'set'
+
+file_path = File.expand_path("../day-09-input.txt", __FILE__)
+input     = File.read(file_path)
+
+hx = hy = 0
+tx = ty = 0
+
+visited = [[tx, ty]].to_set
+
+input.each_line do |line|
+  dir, v = line.split
+  v = v.to_i
+
+  v.times do
+    case dir
+    when "R"
+      hx += 1
+    when "L"
+      hx -= 1
+    when "U"
+      hy += 1
+    when "D"
+      hy -= 1
+    end
+
+    # neighbour check
+    next if (hx - tx).abs <= 1 && (hy - ty).abs <= 1
+
+    if hy != ty
+      ty += (hy - ty).positive? ? 1 : -1
+    end
+
+    if hx != tx
+      tx += (hx - tx).positive? ? 1 : -1
+    end
+
+    visited << [tx, ty]
+  end
+end
+
+puts visited.count

2022/day-09/day-09-input.txt

@@ -0,0 +1,47 @@
+#!/usr/bin/env ruby
+
+require 'set'
+
+file_path = File.expand_path("../day-09-input.txt", __FILE__)
+input     = File.read(file_path)
+
+# Head knot is at index 0
+knots = Array.new(10) { [0, 0] }
+
+visited = [knots[-1].clone].to_set
+
+input.each_line do |line|
+  dir, v = line.split
+  v = v.to_i
+
+  head = knots[0]
+  v.times do
+    case dir
+    when "R"
+      head[0] += 1
+    when "L"
+      head[0] -= 1
+    when "U"
+      head[1] += 1
+    when "D"
+      head[1] -= 1
+    end
+
+    knots.each_cons(2) do |head, tail|
+      # neighbour check
+      next if (head[0] - tail[0]).abs <= 1 && (head[1] - tail[1]).abs <= 1
+
+      if head[1] != tail[1]
+        tail[1] += (head[1] - tail[1]).positive? ? 1 : -1
+      end
+
+      if head[0] != tail[0]
+        tail[0] += (head[0] - tail[0]).positive? ? 1 : -1
+      end
+    end
+
+    visited << knots[-1].clone
+  end
+end
+
+puts visited.count