2019: Day 2 Part 1

2019/day2/part1.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+program = File.read(File.join(__dir__, 'input'))
+
+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
+    else
+      raise StandardError, "unexpected opcode: #{opcode}"
+    end
+  end
+end
+
+mem = program.split(',').map(&:to_i)
+mem[1] = 12
+mem[2] = 2
+run(mem)
+puts mem[0]