Implement opcodes 3 and 4, naively

lib/intcode/intcode.zig

@@ -80,6 +80,19 @@ pub const Machine = struct {
                 program[@intCast(usize, dest)] = result;
                 self.ip += 4;
             },
+            3 => {
+                const input = self.input.orderedRemove(0);
+                const dest = program[self.ip + 1];
+
+                program[@intCast(usize, dest)] = input;
+                self.ip += 2;
+            },
+            4 => {
+                const output = program[@intCast(usize, program[self.ip + 1])];
+
+                try self.output.append(output);
+                self.ip += 2;
+            },
             99 => {
                 self.ip += 1;
                 return false;
@@ -139,7 +152,7 @@ test "day 2 example 5" {
 
 test "day 5 example 1" {
     var before: [5]i32 = .{ 3, 0, 4, 0, 99 };
-    var after = before;
+    var after: [5]i32 = .{ 666, 0, 4, 0, 99 };
     var machine = try Machine.init(test_allocator, before[0..before.len]);
 
     try machine.input.append(666);