Day 19

15/main.go

@@ -67,9 +67,7 @@ func explore(vm *intcode.VirtualMachine) (grid [100][100]tile, stepsToOxygen int
 				}
 
 				vmp := s.vm.Clone()
-				go vmp.Run()
-				vmp.Input <- int(d)
-				state := <-vmp.Output
+				state := *vmp.RunForInput(int(d))
 
 				if state == 0 {
 					grid[yp][xp] = wall

19/answers.txt

@@ -0,0 +1,2 @@
+141
+15641348

19/input.txt

@@ -0,0 +1 @@
+109,424,203,1,21102,11,1,0,1105,1,282,21102,1,18,0,1105,1,259,1201,1,0,221,203,1,21101,0,31,0,1105,1,282,21102,38,1,0,1106,0,259,21001,23,0,2,22101,0,1,3,21101,0,1,1,21102,1,57,0,1105,1,303,2101,0,1,222,21001,221,0,3,20102,1,221,2,21102,259,1,1,21101,80,0,0,1106,0,225,21101,0,111,2,21102,1,91,0,1105,1,303,2102,1,1,223,20101,0,222,4,21102,1,259,3,21102,1,225,2,21102,1,225,1,21101,0,118,0,1105,1,225,20101,0,222,3,21102,148,1,2,21102,1,133,0,1106,0,303,21202,1,-1,1,22001,223,1,1,21102,148,1,0,1106,0,259,2101,0,1,223,20102,1,221,4,21001,222,0,3,21101,0,17,2,1001,132,-2,224,1002,224,2,224,1001,224,3,224,1002,132,-1,132,1,224,132,224,21001,224,1,1,21101,0,195,0,106,0,109,20207,1,223,2,20102,1,23,1,21102,-1,1,3,21101,0,214,0,1105,1,303,22101,1,1,1,204,1,99,0,0,0,0,109,5,2102,1,-4,249,22101,0,-3,1,21202,-2,1,2,21202,-1,1,3,21102,1,250,0,1105,1,225,22102,1,1,-4,109,-5,2106,0,0,109,3,22107,0,-2,-1,21202,-1,2,-1,21201,-1,-1,-1,22202,-1,-2,-2,109,-3,2105,1,0,109,3,21207,-2,0,-1,1206,-1,294,104,0,99,22102,1,-2,-2,109,-3,2106,0,0,109,5,22207,-3,-4,-1,1206,-1,346,22201,-4,-3,-4,21202,-3,-1,-1,22201,-4,-1,2,21202,2,-1,-1,22201,-4,-1,1,21202,-2,1,3,21101,0,343,0,1105,1,303,1105,1,415,22207,-2,-3,-1,1206,-1,387,22201,-3,-2,-3,21202,-2,-1,-1,22201,-3,-1,3,21202,3,-1,-1,22201,-3,-1,2,21201,-4,0,1,21102,384,1,0,1106,0,303,1105,1,415,21202,-4,-1,-4,22201,-4,-3,-4,22202,-3,-2,-2,22202,-2,-4,-4,22202,-3,-2,-3,21202,-4,-1,-2,22201,-3,-2,1,21202,1,1,-4,109,-5,2106,0,0

19/main.go

@@ -0,0 +1,54 @@
+package main
+
+import (
+	"fmt"
+	"github.com/csmith/aoc-2019/common"
+	"github.com/csmith/aoc-2019/intcode"
+)
+
+const shipSize = 100
+
+func main() {
+	input := common.ReadCsvAsInts("19/input.txt")
+	vm := intcode.NewVirtualMachine(make([]int, len(input)))
+
+	var endPositions [shipSize]int
+	endIndex := 0
+
+	sum := 0
+	lastStart := 0
+	for y := 0; ; y++ {
+		first := 0
+
+		for x := lastStart; ; x++ {
+			vm.Reset(input)
+			if *vm.RunForInput(x, y) == 1 {
+				if first == 0 {
+					first = x
+				}
+				if x < 50 && y < 50 {
+					sum++
+				}
+			} else if first > 0 || y < 50 && x > 50 {
+				// For y < 50 if we hit x > 50 without finding the beam, assume it's not there. (The beam isn't
+				// continuous at the start, there's a couple of blanks).
+
+				if x-first >= shipSize-1 {
+					previousEnd := endPositions[endIndex]
+
+					if previousEnd-shipSize >= first-1 {
+						fmt.Println(sum)
+						fmt.Println((previousEnd-shipSize)*10000 + (y - 100))
+						return
+					}
+
+					endPositions[endIndex] = x
+					endIndex = (endIndex + 1) % shipSize
+				}
+				break
+			}
+		}
+
+		lastStart = first
+	}
+}

intcode/ops.go

@@ -45,13 +45,26 @@ func mulOpcode(vm *VirtualMachine, arg1, arg2, arg3 *int) {
 
 // readOpCode reads a value from the input stream and stores it at the memory address given by arg 1.
 func readOpCode(vm *VirtualMachine, arg1, _, _ *int) {
-	*arg1 = <-vm.Input
+	if vm.inputIndex < len(vm.input) {
+		// Read from pre-provided values
+		*arg1 = vm.input[vm.inputIndex]
+		vm.inputIndex++
+	} else {
+		*arg1 = <-vm.Input
+	}
+
 	vm.ip += 2
 }
 
 // writeOpCode writes the value specified by the first argument to the output stream.
 func writeOpCode(vm *VirtualMachine, arg1, _, _ *int) {
-	vm.Output <- *arg1
+	if len(vm.input) > 0 {
+		// Running to get the value of some input, provide the output and halt
+		vm.output = arg1
+		vm.Halted = true
+	} else {
+		vm.Output <- *arg1
+	}
 	vm.ip += 2
 }
 

intcode/vm.go

@@ -10,12 +10,15 @@ const (
 
 // VirtualMachine is an IntCode virtual machine.
 type VirtualMachine struct {
-	ip     int
-	rb     int
-	Memory []int
-	Halted bool
-	Input  chan int
-	Output chan int
+	ip         int
+	rb         int
+	Memory     []int
+	Halted     bool
+	Input      chan int
+	Output     chan int
+	input      []int
+	inputIndex int
+	output     *int
 }
 
 // NewVirtualMachine creates a new IntCode virtual machine, initialised to the given slice of memory.
@@ -36,15 +39,39 @@ func (vm *VirtualMachine) Clone() *VirtualMachine {
 	copy(memory, vm.Memory)
 
 	return &VirtualMachine{
-		ip:     vm.ip,
-		rb:     vm.rb,
-		Memory: memory,
-		Halted: vm.Halted,
-		Input:  make(chan int, 1),
-		Output: make(chan int, 1),
+		ip:         vm.ip,
+		rb:         vm.rb,
+		Memory:     memory,
+		Halted:     vm.Halted,
+		Input:      make(chan int, 1),
+		Output:     make(chan int, 1),
+		input:      vm.input,
+		inputIndex: vm.inputIndex,
+		output:     vm.output,
 	}
 }
 
+// Run repeatedly executes instructions until the VM produces output or halts.
+//
+// The given values will be provided as input whenever a read opcode is executed;
+// any further reads before an output will fallback to reading from the Input
+// channel.
+//
+// If the machine halts instead of outputting a number, this function will return
+// nil.
+func (vm *VirtualMachine) RunForInput(input ...int) *int {
+	vm.inputIndex = 0
+	vm.input = input
+	vm.Run()
+
+	// Reset the halted state so we can carry on running, if required
+	if vm.output != nil {
+		vm.Halted = false
+	}
+
+	return vm.output
+}
+
 // Run repeatedly executes instructions until the VM halts.
 func (vm *VirtualMachine) Run() {
 	var args [3]*int
@@ -98,5 +125,8 @@ func (vm *VirtualMachine) Reset(memory []int) {
 
 	vm.ip = 0
 	vm.rb = 0
+	vm.input = nil
+	vm.inputIndex = 0
+	vm.output = nil
 	vm.Halted = false
 }