willow.go

// https://classroom.google.com/c/NTU0OTE4MjA4NzMw/p/NTAyNDg0NzYyNjQ2/details

package main

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

func printError(msg string) {
	fmt.Fprintln(os.Stderr, msg)
	os.Exit(1)
}

func hdl(err error, msg string) {
	if err != nil {
		printError(msg)
	}
}

// Parse the "T N" header to return T, the number of days Willow spends playing
// per box. N is useless since we can already look at the length of the input.
func parseHeader(header string) int {
	split := strings.Split(header, " ")

	T, err := strconv.Atoi(split[0])
	hdl(err, "Invalid input.")

	return T
}

// Return Willow's playing day buffer overlap
func getDayOverlap(s *bufio.Scanner, playsPerBox int) int {
	playBuffer := 0

	for s.Scan() {
		entry := s.Text()

		if entry == "B" {
			playBuffer += playsPerBox

		} else if entry != "E" {
			printError("Invalid input. Use one file per chain of days.")
		}

		if playBuffer > 0 {
			playBuffer--
		}
	}

	return playBuffer
}

func main() {
	if len(os.Args) != 2 {
		printError("Usage: willow input.txt.")
	}

	f, err := os.Open(os.Args[1])
	hdl(err, "Couldn't open input.")

	s := bufio.NewScanner(f)
	s.Scan()
	header := s.Text()

	playsPerBox := parseHeader(header)
	overlap := getDayOverlap(s, playsPerBox)

	fmt.Println(overlap)
}