aoc2021/sixteen/bits.go

package sixteen

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

const (
	literalType  = 4
	lengthType15 = 0
	lengthType11 = 1
)

var hexToBin = map[string]string{
	"0": "0000",
	"1": "0001",
	"2": "0010",
	"3": "0011",
	"4": "0100",
	"5": "0101",
	"6": "0110",
	"7": "0111",
	"8": "1000",
	"9": "1001",
	"A": "1010",
	"B": "1011",
	"C": "1100",
	"D": "1101",
	"E": "1110",
	"F": "1111",
}

type packet struct {
	packet     string
	version    int
	typeID     int
	content    int
	subpackets []packet
}

func (p *packet) versionSum() int {
	sum := p.version

	for _, s := range p.subpackets {
		sum += s.versionSum()
	}

	return sum
}

func hexToBinary(input string) string {
	output := ""
	for _, r := range input {
		output += hexToBin[string(r)]
	}

	return output
}

func parseHex(input string) packet {
	binary := hexToBinary(input)
	return parse(binary)
}

func parse(input string) packet {
	b := packet{}
	b.packet = input

	b.version, b.typeID = parseVersionType(input)
	content := input[6:]

	switch b.typeID {
	case literalType:
		b.content, _ = parseLiteral(content)
	default:
		b.subpackets, _ = parseOperator(content)
	}

	return b
}

func parseVersionType(input string) (int, int) {
	var version, typeID string
	if count, err := fmt.Sscanf(input, "%3s%3s", &version, &typeID); count != 2 || err != nil {
		fmt.Println("Unable to parse", input, err)
		return -1, -1
	}

	v, err := strconv.ParseInt(version, 2, 64)
	if err != nil {
		fmt.Println("Unable to parse version from", version, err)
		return -1, -1
	}

	t, err := strconv.ParseInt(typeID, 2, 64)
	if err != nil {
		fmt.Println("Unable to parse type from", typeID, err)
		return -1, -1
	}

	return int(v), int(t)
}

func parsePackets(input string) []packet {
	packets := []packet{}

	remaining := input
	for remaining != "" {
		version, typeID := parseVersionType(remaining)

		p := packet{
			version: version,
			typeID:  typeID,
		}

		switch p.typeID {
		case literalType:
			value, length := parseLiteral(remaining[6:])
			p.content = value
			p.packet = remaining[:length+6]
			remaining = remaining[length+6:]
		default:
			l := 0
			p.subpackets, l = parseOperator(remaining[6:])
			remaining = remaining[l+7:]
		}

		packets = append(packets, p)
	}

	return packets
}

func parseNPackets(input string, count int) ([]packet, int) {
	length := len(input)
	packets := []packet{}

	remaining := input
	for len(packets) != count {
		version, typeID := parseVersionType(remaining)

		p := packet{
			version: version,
			typeID:  typeID,
		}

		switch p.typeID {
		case literalType:
			value, length := parseLiteral(remaining[6:])
			p.content = value
			p.packet = remaining[:length+6]
			remaining = remaining[length+6:]
		default:
			l := 0
			p.subpackets, l = parseOperator(remaining[6:])
			remaining = remaining[l+7:]
		}

		packets = append(packets, p)
	}

	return packets, length - len(remaining)
}

func parseOperator(input string) ([]packet, int) {
	length := 0
	subPackets := []packet{}
	var lType int
	var remainder string
	if count, err := fmt.Sscanf(input, "%1d%s", &lType, &remainder); count != 2 || err != nil {
		fmt.Println("Unable to parse operator type", input)
		return subPackets, length
	}

	switch lType {
	case lengthType15:
		lengthBits, _ := strconv.ParseInt(string(remainder[:15]), 2, 64)
		subs := parsePackets(remainder[15 : 15+lengthBits])
		subPackets = append(subPackets, subs...)
		length = 15 + int(lengthBits)
	case lengthType11:
		lengthBits, _ := strconv.ParseInt(string(remainder[:11]), 2, 64)
		subs, l := parseNPackets(remainder[11:], int(lengthBits))
		subPackets = append(subPackets, subs...)
		length = l
	}

	return subPackets, length
}

func parseLiteral(input string) (int, int) {
	literal := ""
	length := 0
	for i := 0; i < len(input); i += 5 {
		literal += string(input[i+1]) + string(input[i+2]) + string(input[i+3]) + string(input[i+4])
		length += 5

		if input[i] == '0' {
			break
		}
	}

	v, err := strconv.ParseInt(literal, 2, 64)
	if err != nil {
		fmt.Println("Unable to parse", literal, err)
		return 0, -1
	}

	return int(v), length
}

func load(filename string) packet {
	b := packet{}

	file, err := os.Open(filename)
	if err != nil {
		return b
	}
	defer file.Close()
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		b = parseHex(scanner.Text())
	}
	return b
}