AdventOfCode2021/16/main.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"time"
)

func main() {
	start := time.Now()
	partOne()
	duration := time.Since(start)
	partTwo()
	duration2 := time.Since(start)
	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
}

var hexMap = map[rune][]uint8{
	'0': {0, 0, 0, 0},
	'1': {0, 0, 0, 1},
	'2': {0, 0, 1, 0},
	'3': {0, 0, 1, 1},
	'4': {0, 1, 0, 0},
	'5': {0, 1, 0, 1},
	'6': {0, 1, 1, 0},
	'7': {0, 1, 1, 1},
	'8': {1, 0, 0, 0},
	'9': {1, 0, 0, 1},
	'A': {1, 0, 1, 0},
	'B': {1, 0, 1, 1},
	'C': {1, 1, 0, 0},
	'D': {1, 1, 0, 1},
	'E': {1, 1, 1, 0},
	'F': {1, 1, 1, 1},
}

func makeScanner(test bool) *bufio.Scanner {
	var f *os.File
	if test {
		f, _ = os.Open("inputs/testinput")
	} else {
		f, _ = os.Open("inputs/input")
	}
	reader := bufio.NewReader(f)
	return bufio.NewScanner(reader)
}

func parseNumber(stream []uint8, length int) int {
	result := int(0)
	for i := 0; i < length; i++ {
		result += int(stream[i]) << (length - 1 - i)
	}
	return result
}

type packet struct {
	version       int
	typeID        int
	subPackets    []packet
	encodedNumber int
}

func getPacketVersion(stream []uint8) int {
	return parseNumber(stream, 3)
}

func getPacketType(stream []uint8) int {
	return parseNumber(stream, 3)
}

func getSubpacketLength(t uint8, stream []uint8) (int, int) {
	if t == 0 {
		return 15, parseNumber(stream, 15)
	}
	if t == 1 {
		return 11, parseNumber(stream, 11)
	}
	return 0, 0
}

func parsePayload(stream []uint8) (int, int) {
	num := []uint8{}
	pos := 0
	chars := 0
	for {
		currentsegment := stream[pos : pos+5]
		chars += 4
		num = append(num, currentsegment[1:5]...)
		pos += 5
		if currentsegment[0] == 0 {
			break
		}
	}
	return parseNumber(num, chars), pos
}

func parsePackets(stream []uint8) (int, packet) {
	if len(stream) <= 7 {
		return 0, packet{}
	}
	parsedPacket := packet{}
	parsedPacket.version = getPacketVersion(stream[0:3])
	parsedPacket.typeID = getPacketType(stream[3:6])
	if parsedPacket.typeID == 4 {
		encoded, consumed := parsePayload(stream[6:])
		parsedPacket.encodedNumber = encoded
		return consumed + 6, parsedPacket // 6 is packet header length
	} else {
		parsed := 0
		size, subpacketlength := getSubpacketLength(stream[6], stream[7:])
		for {
			consumed, subs := parsePackets(stream[7+size+parsed:])
			if consumed == 0 {
				return parsed + 7 + size, parsedPacket
			}
			parsedPacket.subPackets = append(parsedPacket.subPackets, subs)
			parsed += consumed
			if size == 11 && len(parsedPacket.subPackets) == subpacketlength {
				return parsed + 7 + size, parsedPacket

			} else if size == 15 && parsed > subpacketlength {
				return parsed + 7 + size, parsedPacket
			}
		}
	}
}

func countVersions(pac packet) int {
	i := int(pac.version)
	for _, p := range pac.subPackets {
		i += countVersions(p)
	}
	return i
}

func partOne() {
	scanner := makeScanner(false)

	scanner.Scan()
	line := scanner.Text()
	stream := []uint8{}
	for _, hex := range line {
		stream = append(stream, hexMap[hex]...)
	}
	_, parsedPacket := parsePackets(stream)
	fmt.Println(countVersions(parsedPacket))
}

func solve(p packet) int {
	switch p.typeID {
	case 0: // sum
		if len(p.subPackets) == 1 {
			return solve(p.subPackets[0])
		} else {
			acc := 0
			for _, v := range p.subPackets {
				acc += solve(v)
			}
			return acc
		}
	case 1: // product
		if len(p.subPackets) == 1 {
			return solve(p.subPackets[0])
		} else {
			acc := solve(p.subPackets[0])
			for _, v := range p.subPackets[1:] {
				acc *= solve(v)
			}
			return acc
		}
	case 2: // min
		if len(p.subPackets) == 1 {
			return solve(p.subPackets[0])
		} else {
			acc := solve(p.subPackets[0])
			for _, v := range p.subPackets[1:] {
				t := solve(v)
				if t < acc {
					acc = t
				}
			}
			return acc
		}
	case 3: // max
		if len(p.subPackets) == 1 {
			return solve(p.subPackets[0])
		} else {
			acc := solve(p.subPackets[0])
			for _, v := range p.subPackets[1:] {
				t := solve(v)
				if t > acc {
					acc = t
				}
			}
			return acc
		}
	case 4: // number
		return p.encodedNumber
	case 5: // >
		if len(p.subPackets) != 2 {
			panic(fmt.Sprintf("recevied type 5 packet with %d subpackets", len(p.subPackets)))
		}
		if solve(p.subPackets[0]) > solve(p.subPackets[1]) {
			return 1
		} else {
			return 0
		}
	case 6: // <
		if len(p.subPackets) != 2 {
			panic(fmt.Sprintf("recevied type 6 packet with %d subpackets", len(p.subPackets)))
		}
		if solve(p.subPackets[0]) < solve(p.subPackets[1]) {
			return 1
		} else {
			return 0
		}
	case 7: // ==
		if len(p.subPackets) != 2 {
			panic(fmt.Sprintf("recevied type 7 packet with %d subpackets", len(p.subPackets)))
		}
		if solve(p.subPackets[0]) == solve(p.subPackets[1]) {
			return 1
		} else {
			return 0
		}
	default:
		panic("unknown packet type")
	}
}

func partTwo() {
	scanner := makeScanner(false)

	scanner.Scan()
	line := scanner.Text()
	stream := []uint8{}
	for _, hex := range line {
		stream = append(stream, hexMap[hex]...)
	}
	_, parsedPacket := parsePackets(stream)
	fmt.Println(solve(parsedPacket))
}