Day 23 solution

This one takes around a second to arrive at the first answer and around 15 seconds to arrive at the second answer. I don't know why, since I'm just running the given program as fast as possible (is my interpreter slow?). Go channels should be about as fast as we can get here. Maybe it would actually run faster if everyone stopped and processed their inputs at the same time or something? I dunno.

Part 2 was pretty simple, though I feel like my idle detection could be improved. Seems to work, though.

days/23.go

@@ -0,0 +1,170 @@
+package days
+
+import (
+	"fmt"
+	"sync"
+
+	u "parnic.com/aoc2019/utilities"
+)
+
+type day23Computer struct {
+	program            u.IntcodeProgram
+	id                 int
+	packetQueue        chan u.Vec2[int64]
+	outputStep         int
+	nextPacketDest     int
+	sendingPacket      u.Vec2[int64]
+	hasQueuedPacket    bool
+	lastReceivedPacket u.Vec2[int64]
+	idle               bool
+}
+
+func (d Day23) makeComputer(id int) *day23Computer {
+	c := &day23Computer{
+		program:     d.program.Copy(),
+		id:          id,
+		packetQueue: make(chan u.Vec2[int64]),
+		idle:        true,
+	}
+
+	return c
+}
+
+type Day23 struct {
+	program u.IntcodeProgram
+}
+
+func (d *Day23) Parse() {
+	d.program = u.LoadIntcodeProgram("23p")
+}
+
+func (d Day23) Num() int {
+	return 23
+}
+
+func (d Day23) initComputers() []*day23Computer {
+	computers := make([]*day23Computer, 50)
+	for i := range computers {
+		computers[i] = d.makeComputer(i)
+	}
+	return computers
+}
+
+func (d Day23) execComputers(computers []*day23Computer, nat chan u.Vec2[int64]) *sync.WaitGroup {
+	wg := &sync.WaitGroup{}
+	wg.Add(len(computers))
+	for _, c := range computers {
+		go func(c *day23Computer) {
+			bootedUp := false
+			c.program.RunIn(func(inputStep int) int64 {
+				if !bootedUp {
+					bootedUp = true
+					return int64(c.id)
+				}
+
+				if c.hasQueuedPacket {
+					// fmt.Printf("  %d finished processing packet %v\n", c.id, c.lastReceivedPacket)
+					c.hasQueuedPacket = false
+					return c.lastReceivedPacket.Y
+				}
+
+				select {
+				case c.lastReceivedPacket = <-c.packetQueue:
+					// fmt.Printf("computer %d received packet %v\n", c.id, packet)
+					c.hasQueuedPacket = true
+					return c.lastReceivedPacket.X
+				default:
+					c.idle = true
+					return -1
+				}
+			}, func(val int64, state u.IntcodeProgramState) {
+				c.idle = false
+				switch c.outputStep {
+				case 0:
+					c.nextPacketDest = int(val)
+				case 1:
+					c.sendingPacket.X = val
+				case 2:
+					c.sendingPacket.Y = val
+
+					if c.nextPacketDest == 255 {
+						// fmt.Printf("computer %d sending %v to 255\n", c.id, c.sendingPacket)
+						nat <- c.sendingPacket
+					} else {
+						// fmt.Printf("computer %d sending %v to computer %d\n", c.id, c.sendingPacket, c.nextPacketDest)
+						computers[c.nextPacketDest].packetQueue <- c.sendingPacket
+					}
+				}
+
+				c.outputStep = (c.outputStep + 1) % 3
+			})
+
+			wg.Done()
+		}(c)
+	}
+
+	return wg
+}
+
+func (d *Day23) Part1() string {
+	computers := d.initComputers()
+	natChan := make(chan u.Vec2[int64])
+	wg := d.execComputers(computers, natChan)
+
+	answer := <-natChan
+	for _, c := range computers {
+		c.program.Stop()
+	}
+	// not really necessary, but let's make sure they all shut down in case
+	// we're running all days at once
+	wg.Wait()
+
+	return fmt.Sprintf("First packet sent to 255 Y value: %s%d%s", u.TextBold, answer.Y, u.TextReset)
+}
+
+func (d *Day23) Part2() string {
+	computers := d.initComputers()
+	natChan := make(chan u.Vec2[int64])
+	wg := d.execComputers(computers, natChan)
+
+	answerChan := make(chan int64)
+
+	go func() {
+		var currVal u.Vec2[int64]
+		var lastVal u.Vec2[int64]
+		hasReceived := false
+		for {
+			select {
+			case currVal = <-natChan:
+				hasReceived = true
+			default:
+			}
+
+			allIdle := true
+			for _, c := range computers {
+				if !c.idle {
+					allIdle = false
+					break
+				}
+			}
+
+			if allIdle && hasReceived {
+				// fmt.Printf("all idle, sending %v to computer 0\n", currVal)
+				if lastVal.Y == currVal.Y {
+					// fmt.Printf("found answer? %d\n", currVal.Y)
+					answerChan <- currVal.Y
+				}
+				computers[0].packetQueue <- currVal
+				lastVal = currVal
+			}
+		}
+	}()
+
+	answer := <-answerChan
+	for _, c := range computers {
+		c.program.Stop()
+	}
+	wg.Wait()
+
+	return fmt.Sprintf("First Y value sent to the NAT twice in a row: %s%d%s", u.TextBold, answer, u.TextReset)
+}

main.go

@@ -56,6 +56,7 @@ var dayMap = []day{
 	&days.Day20{},
 	&days.Day21{},
 	&days.Day22{},
+	&days.Day23{},
 }
 
 func main() {