[2017][ruby][3.x] speedrun

2017/input/day_03.txt

@@ -0,0 +1 @@
+361527

2017/ruby/day_03.rb

@@ -0,0 +1,40 @@
+input = ARGF.read.to_i
+
+dir = [1,0]
+
+def next_dir(dir)
+  case dir
+  when [1,0]
+    [0,1]
+  when [0,1]
+    [-1,0]
+  when [-1,0]
+    [0,-1]
+  when [0,-1]
+    [1,0]
+  else
+    raise "invalid dir: #{dir}"
+  end
+end
+
+grid = Hash.new(0)
+grid[[0,0]] = 1
+
+def next_value(grid, x, y)
+  [[-1, 1],[0, 1],[1,1],
+   [-1, 0],       [1,0],
+   [-1,-1],[0,-1],[1,-1]].map {|i,j| grid[[x+i,y+j]]}.sum
+end
+
+current = [0,0]
+loop do
+  next_square = current.zip(dir).map {|a,b| a + b }
+  value = next_value(grid, *next_square)
+  puts "#{current}: #{value}"
+  exit if value > input
+  grid[next_square] = value
+  current = next_square
+  dir = next_dir(dir) if grid[current.zip(next_dir(dir)).map {|a,b| a + b }] == 0
+end
+
+p next_value(grid, 1,0)