Explain and implement logic

Programs coded into a machine that runs a program that's coded into a machine that runs a program. I think this is how Javascript got invented or something.

days/17.go

@@ -48,6 +48,7 @@ type Day17 struct {
 
 func (d *Day17) Parse() {
 	d.program = u.LoadIntcodeProgram("17p")
+	// d.program.SetDebugASCIIPrint(true)
 }
 
 func (d Day17) Num() int {
@@ -388,9 +389,8 @@ func (d *Day17) Part2() string {
 	row := 0
 	var outputState int
 	var lastOutput int64
-	var instructionStr string
 	d.program.RunIn(func(inputStep int) int64 {
-		return int64(instructionStr[inputStep-1])
+		panic("unexpected read")
 	}, func(val int64, state u.IntcodeProgramState) {
 		rVal := rune(val)
 		if outputState == 0 {
@@ -401,7 +401,7 @@ func (d *Day17) Part2() string {
 
 		if rVal == '\n' && lastOutput == '\n' {
 			if outputState == 0 {
-				instructionStr = beforeGrid.solvePath(beforeBotLocation, beforeBotFacing)
+				d.program.FeedInputString(beforeGrid.solvePath(beforeBotLocation, beforeBotFacing))
 			}
 			outputState++
 			row = 0

days/21.go

@@ -0,0 +1,85 @@
+package days
+
+import (
+	"fmt"
+	"strings"
+
+	u "parnic.com/aoc2019/utilities"
+)
+
+type Day21 struct {
+	program u.IntcodeProgram
+}
+
+func (d *Day21) Parse() {
+	d.program = u.LoadIntcodeProgram("21p")
+	// d.program.SetDebugASCIIPrint(true)
+}
+
+func (d Day21) Num() int {
+	return 21
+}
+
+func (d *Day21) Part1() string {
+	// if there's any hole up to 3 ahead of us but there's ground where we'd land if we jumped
+	// (a jump takes 4 spaces), go ahead and jump
+	cmds := []string{
+		// check if a hole at 1 or 2 ahead
+		"NOT A T",
+		"NOT B J",
+		// store that result in J
+		"OR T J",
+		// check if a hole at 3 ahead
+		"NOT C T",
+		// store hole in 1, 2, or 3 in T
+		"OR J T",
+		// set J true if hole in 1, 2, or 3
+		"OR T J",
+		// set J true if also no hole at 4 ahead
+		"AND D J",
+		"WALK",
+	}
+	instructionStr := strings.Join(cmds, "\n") + "\n"
+	d.program.FeedInputString(instructionStr)
+
+	res := d.program.Run()
+
+	return fmt.Sprintf("Hull damage value when walking: %s%d%s", u.TextBold, res, u.TextReset)
+}
+
+func (d *Day21) Part2() string {
+	//   @
+	// #####.#.##.##.###
+	//    ABCDEFGHI
+	// using the first program, this kills us. if we jump, we land at D and H becomes our new D, so it won't jump again.
+	// but if we waited to jump until we got one more ahead, we'd be ok.
+	// so now we want to know essentially the same thing as part 1, but also if our multiple (immediate second jump) would be successful.
+	// in problem terms, that's: if there's a hole at 1 or 2 ahead, and there's a hole at C with ground at H, and there's ground at D.
+	// so now for the above example we'd wait to jump until here:
+	//     @
+	// #####.#.##.##.###
+	//      ABCDEFGHI
+	// and all will be well.
+	cmds := []string{
+		// check if a hole at 1 or 2 ahead
+		"NOT A J",
+		"NOT B T",
+		// store that result in J
+		"OR T J",
+		// check if a hole at 3 ahead...
+		"NOT C T",
+		// and ground at 8 ahead (so we can immediately jump again if needed)...
+		"AND H T",
+		// combine those into J
+		"OR T J",
+		// and ensure we also still have a place to land if we jumped right away
+		"AND D J",
+		"RUN",
+	}
+	instructionStr := strings.Join(cmds, "\n") + "\n"
+	d.program.FeedInputString(instructionStr)
+
+	res := d.program.Run()
+
+	return fmt.Sprintf("Hull damage value when running: %s%d%s", u.TextBold, res, u.TextReset)
+}

main.go

@@ -54,6 +54,7 @@ var dayMap = []day{
 	&days.Day18{},
 	&days.Day19{},
 	&days.Day20{},
+	&days.Day21{},
 }
 
 func main() {

utilities/intcode.go

@@ -28,6 +28,8 @@ type IntcodeProgram struct {
 	program       []int64
 	relativeBase  int
 	haltRequested bool
+	printASCII    bool
+	feedInput     []rune
 }
 
 type IntcodeProgramState struct {
@@ -140,14 +142,15 @@ func (p *IntcodeProgram) Reset() {
 	p.relativeBase = 0
 }
 
-func (p *IntcodeProgram) Run() {
+func (p *IntcodeProgram) Run() int64 {
-	p.RunIn(func(int) int64 { return 0 }, func(int64, IntcodeProgramState) {})
+	return p.RunIn(func(int) int64 { return 0 }, func(int64, IntcodeProgramState) {})
 }
 
-func (p *IntcodeProgram) RunIn(inputFunc ProvideInputFunc, outputFunc ReceiveOutputFunc) {
+func (p *IntcodeProgram) RunIn(inputFunc ProvideInputFunc, outputFunc ReceiveOutputFunc) int64 {
 	p.init()
 
 	inputsRequested := 0
+	lastOutput := int64(0)
 	for instructionPointer := 0; instructionPointer < len(p.program) && !p.haltRequested; {
 		instruction := p.GetMemory(instructionPointer)
 		instructionPointer++
@@ -184,13 +187,28 @@ func (p *IntcodeProgram) RunIn(inputFunc ProvideInputFunc, outputFunc ReceiveOut
 		case opInput:
 			inputsRequested++
 			param1 := p.GetMemory(instructionPointer)
-			p.setMemory(int(param1), inputFunc(inputsRequested), paramModes[0])
+			var inputVal int64
+			if len(p.feedInput) > 0 {
+				inputVal = int64(p.feedInput[0])
+				p.feedInput = p.feedInput[1:]
+			} else {
+				inputVal = inputFunc(inputsRequested)
+			}
+			if p.printASCII && inputVal <= 255 {
+				fmt.Printf("%c", rune(inputVal))
+			}
+			p.setMemory(int(param1), inputVal, paramModes[0])
 
 			instructionPointer += 1
 
 		case opOutput:
 			param1 := p.GetMemory(instructionPointer)
-			outputFunc(p.getParamValue(int(param1), paramModes[0]), p.makeState(instructionPointer))
+			param1Val := p.getParamValue(int(param1), paramModes[0])
+			if p.printASCII && param1Val <= 255 {
+				fmt.Printf("%c", rune(param1Val))
+			}
+			outputFunc(param1Val, p.makeState(instructionPointer))
+			lastOutput = param1Val
 
 			instructionPointer += 1
 
@@ -256,8 +274,19 @@ func (p *IntcodeProgram) RunIn(inputFunc ProvideInputFunc, outputFunc ReceiveOut
 	}
 
 	p.haltRequested = false
+
+	return lastOutput
 }
 
 func (p *IntcodeProgram) Stop() {
 	p.haltRequested = true
 }
+
+func (p *IntcodeProgram) SetDebugASCIIPrint(enable bool) {
+	p.printASCII = enable
+}
+
+func (p *IntcodeProgram) FeedInputString(str string) {
+	p.feedInput = make([]rune, len(str))
+	copy(p.feedInput, []rune(str))
+}