[2024] Solution for Day 17

Author: kfarnung

2024/day17/main.go

@@ -0,0 +1,232 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strings"
+
+	"github.com/kfarnung/advent-of-code/2024/lib"
+)
+
+type computer struct {
+	registers registers
+	program   []int32
+	output    func(value int32) bool
+}
+
+type registers struct {
+	a, b, c int64
+	ip      int
+}
+
+func (c computer) LiteralOperand() int64 {
+	return int64(c.program[c.registers.ip+1])
+}
+
+func (c computer) ComboOperand() int64 {
+	operand := c.LiteralOperand()
+	switch operand {
+	case 0:
+		fallthrough
+	case 1:
+		fallthrough
+	case 2:
+		fallthrough
+	case 3:
+		return operand
+	case 4:
+		return c.registers.a
+	case 5:
+		return c.registers.b
+	case 6:
+		return c.registers.c
+	}
+
+	log.Fatalf("Invalid operand: %d", operand)
+	return 0
+}
+
+func (c computer) Divide() int64 {
+	return int64(int64(c.registers.a) / intPow(2, int64(c.ComboOperand())))
+}
+
+func (c *computer) Run() error {
+	seenStates := make(map[registers]bool)
+
+	for c.registers.ip < len(c.program) {
+		if seenStates[c.registers] {
+			return fmt.Errorf("infinite loop detected")
+		}
+
+		seenStates[c.registers] = true
+
+		switch c.program[c.registers.ip] {
+		case 0:
+			// adv
+			c.registers.a = c.Divide()
+			c.registers.ip += 2
+
+		case 1:
+			// bxl
+			c.registers.b = c.registers.b ^ c.LiteralOperand()
+			c.registers.ip += 2
+
+		case 2:
+			// bst
+			c.registers.b = c.ComboOperand() % 8
+			c.registers.ip += 2
+
+		case 3:
+			// jnz
+			if c.registers.a != 0 {
+				c.registers.ip = int(c.LiteralOperand())
+			} else {
+				c.registers.ip += 2
+			}
+
+		case 4:
+			// bxc
+			c.registers.b = c.registers.b ^ c.registers.c
+			c.registers.ip += 2
+
+		case 5:
+			// out
+			if !c.output(int32(c.ComboOperand() % 8)) {
+				return fmt.Errorf("program aborted")
+			}
+
+			c.registers.ip += 2
+
+		case 6:
+			// bdv
+			c.registers.b = c.Divide()
+			c.registers.ip += 2
+
+		case 7:
+			// cdv
+			c.registers.c = c.Divide()
+			c.registers.ip += 2
+		}
+	}
+
+	return nil
+}
+
+func (c *computer) Reset() {
+	c.registers.a = 0
+	c.registers.b = 0
+	c.registers.c = 0
+	c.registers.ip = 0
+}
+
+func part1(input string) string {
+	computer := parseInput(input)
+	var output []int32
+	computer.output = func(value int32) bool {
+		output = append(output, value)
+		return true
+	}
+
+	err := computer.Run()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	outputStrings := make([]string, len(output))
+	for i, val := range output {
+		outputStrings[i] = fmt.Sprintf("%d", val)
+	}
+
+	return strings.Join(outputStrings, ",")
+}
+
+func part2(input string) int64 {
+	computer := parseInput(input)
+	value, err := solve(0, computer.program)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	return value
+}
+
+func solve(current int64, program []int32) (int64, error) {
+	target := program[len(program)-1]
+	for i := int64(0); i < 8; i++ {
+		value := doIteration(current + i)
+		if value == int64(target) {
+			if len(program) == 1 {
+				return current + i, nil
+			}
+
+			next, err := solve((current+i)*8, program[:len(program)-1])
+			if err == nil {
+				return next, nil
+			}
+		}
+	}
+
+	return 0, fmt.Errorf("no solution found")
+}
+
+func doIteration(a int64) int64 {
+	b, c := int64(0), int64(0)
+	b = a % 8
+	b = b ^ 2
+	c = a / intPow(2, b)
+	b = b ^ 3
+	b = b ^ c
+	return b % 8
+}
+
+func intPow(base, exp int64) int64 {
+	if exp == 0 {
+		return 1
+	}
+
+	value := base
+	for i := int64(1); i < exp; i++ {
+		value *= base
+	}
+
+	return value
+}
+
+func parseInput(input string) computer {
+	lines := lib.SplitLines(input)
+
+	a, err := lib.ParseInt[int64](strings.Split(lines[0], ": ")[1])
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	b, err := lib.ParseInt[int64](strings.Split(lines[1], ": ")[1])
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	c, err := lib.ParseInt[int64](strings.Split(lines[2], ": ")[1])
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	programString := strings.Split(lines[4], ": ")[1]
+	program, err := lib.StringSliceToInt32(strings.Split(programString, ","))
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	return computer{registers: registers{a: a, b: b, c: c}, program: program}
+}
+
+func main() {
+	name := os.Args[1]
+	content, err := lib.LoadFileContent(name)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Printf("Part 1: %s\n", part1(content))
+	fmt.Printf("Part 2: %d\n", part2(content))
+}

2024/day17/main_test.go

@@ -0,0 +1,38 @@
+package main
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/kfarnung/advent-of-code/2024/lib"
+	"github.com/stretchr/testify/assert"
+)
+
+var input = strings.Join([]string{
+	"Register A: 729",
+	"Register B: 0",
+	"Register C: 0",
+	"",
+	"Program: 0,1,5,4,3,0",
+	"",
+}, "\n")
+
+func TestPart1(t *testing.T) {
+	// assert.Equal(t, "4,6,3,5,6,3,5,2,1,0", part1(input))
+
+	inputContent, err := lib.GetInputContent()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, "7,1,5,2,4,0,7,6,1", part1(inputContent))
+}
+
+func TestPart2(t *testing.T) {
+	inputContent, err := lib.GetInputContent()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, int64(37222273957364), part2(inputContent))
+}