2019: Day 2 Part 2

2019/day2/part2.rb

@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+def run(mem)
+  pc = 0
+  loop do
+    case mem[pc]
+    when 1
+      r1, r2, r3 = mem[pc+1], mem[pc+2], mem[pc+3]
+      mem[r3] = mem[r1] + mem[r2]
+      pc += 4
+    when 2
+      r1, r2, r3 = mem[pc+1], mem[pc+2], mem[pc+3]
+      mem[r3] = mem[r1] * mem[r2]
+      pc += 4
+    when 99
+      return mem[0]
+    else
+      raise StandardError, "unexpected opcode: #{opcode}"
+    end
+  end
+end
+
+def solve(program)
+  (0...99).each do |noun|
+    (0...99).each do |verb|
+      puts "Trying noun = #{noun}, verb = #{verb} ..."
+      mem = program.clone
+      mem[1] = noun
+      mem[2] = verb
+      output = run(mem)
+      puts "Output: #{output}"
+      if output == 19690720
+        return [noun, verb, 100*noun + verb]
+      end
+    end
+  end
+end
+
+input = File.read(File.join(__dir__, 'input'))
+program = input.split(',').map(&:to_i)
+puts solve(program)