Add day 02: Elevator Keypad

Author: petertseng

02_elevator_keypad.rb

@@ -0,0 +1,47 @@
+parts = [{
+  keypad: [
+    [1, 2, 3],
+    [4, 5, 6],
+    [7, 8, 9],
+  ].map(&:freeze).freeze,
+  admit: ->(row, col) { [row, col].all? { |c| 0 <= c && c <= 2 } }
+}, {
+  keypad: [
+    [nil, nil,  1, nil, nil],
+    [nil,   2,  3,   4, nil],
+    [  5,   6,  7,   8,   9],
+    [nil,  :A, :B,  :C, nil],
+    [nil, nil, :D, nil, nil],
+  ].map(&:freeze).freeze,
+  admit: ->(row, col) { (col - 2).abs + (row - 2).abs <= 2 }
+}].map(&:freeze).freeze
+
+START_AT = 5
+
+input = ARGF.readlines.map(&:freeze).freeze
+
+puts parts.map { |part|
+  keypad = part[:keypad].map(&:freeze).freeze
+  admit = part[:admit]
+
+  row = keypad.index { |x| x.include?(START_AT) }
+  pos = [row, keypad[row].index(START_AT)]
+
+  try = ->(coord:, dir:) {
+    pos[coord] += dir
+    pos[coord] -= dir unless admit[*pos]
+  }
+
+  input.map { |l|
+    l.chomp.each_char { |c|
+      case c
+      when ?L; try[coord: 1, dir: -1]
+      when ?R; try[coord: 1, dir:  1]
+      when ?U; try[coord: 0, dir: -1]
+      when ?D; try[coord: 0, dir:  1]
+      else raise "bad char #{c}"
+      end
+    }
+    keypad[pos[0]][pos[1]]
+  }.join
+}