adventofcode/2020/day05.go

package main

import (
	"fmt"
	"log"
	"os"
	"strconv"
	"strings"

	"git.annabunch.es/annabunches/adventofcode/2020/lib/util"
)

func calculateSeatNumber(input string) int {
	if input == "" {
		return 0
	}

	row, err := strconv.ParseInt(strings.ReplaceAll(strings.ReplaceAll(input[0:7], "F", "0"), "B", "1"), 2, 32)
	if err != nil {
		log.Panicf(err.Error())
	}
	col, err := strconv.ParseInt(strings.ReplaceAll(strings.ReplaceAll(input[7:10], "L", "0"), "R", "1"), 2, 32)
	if err != nil {
		log.Panicf(err.Error())
	}
	return int((row * 8) + col)
}

func main() {
	step := os.Args[1]
	values := util.InputParserStrings(os.Args[2])

	switch step {
	case "1":
		max := 0
		for _, line := range values {
			seatNumber := calculateSeatNumber(line)
			if seatNumber > max {
				max = seatNumber
			}
		}
		fmt.Println("Highest Seat Number:", max)
	case "2":
		// build a map of all seat numbers then just print the ones between 0 and 1024 that don't exist
		seatMap := make(map[int]bool)
		for _, line := range values {
			seatNumber := calculateSeatNumber(line)
			seatMap[seatNumber] = true
		}

		for i := 0; i < 1024; i++ {
			if _, ok := seatMap[i]; !ok {
				fmt.Println("Didn't find seat ", i)
			}
		}
	}
}