advent2022/solutions/day2/day2.go

package day2

import (
	"bufio"
	"fmt"
	"os"

	"golang.org/x/exp/utf8string"
)

type Move = int

const (
	Rock     Move = 1
	Paper         = 2
	Scissors      = 3
)

type Result = int

const (
	Loss Result = 0
	Tie         = 3
	Win         = 6
)

func score(opponent Move, us Move) int {
	switch opponent {
	case Rock:
		switch us {
		case Rock:
			return Rock + Tie
		case Paper:
			return Paper + Win
		case Scissors:
			return Scissors + Loss
		}

	case Paper:
		switch us {
		case Rock:
			return Rock + Loss
		case Paper:
			return Paper + Tie
		case Scissors:
			return Scissors + Win
		}

	case Scissors:
		switch us {
		case Rock:
			return Rock + Win
		case Paper:
			return Paper + Loss
		case Scissors:
			return Scissors + Tie
		}
	}

	fmt.Println("PANIC: Unknown combo: them", opponent, "us", us)
	return 0
}

func compute_move(opponent Move, goal Result) Move {
	switch opponent {
	case Rock:
		switch goal {
		case Loss:
			return Scissors
		case Tie:
			return Rock
		case Win:
			return Paper
		}

	case Paper:
		switch goal {
		case Loss:
			return Rock
		case Tie:
			return Paper
		case Win:
			return Scissors
		}

	case Scissors:
		switch goal {
		case Loss:
			return Paper
		case Tie:
			return Scissors
		case Win:
			return Rock
		}
	}

	fmt.Println("PANIC: Unknown combo: them", opponent, "goal", goal)
	return 0

}

func move(r rune) Move {
	switch r {
	case 'A':
		return Rock
	case 'B':
		return Paper
	case 'C':
		return Scissors
	case 'X':
		return Rock
	case 'Y':
		return Paper
	case 'Z':
		return Scissors
	}
	fmt.Println("PANIC: Unknown character", r)
	return 0
}

func result(r rune) Result {
	switch r {
	case 'X':
		return Loss
	case 'Y':
		return Tie
	case 'Z':
		return Win
	}
	fmt.Println("PANIC: Unknown character for result", r)
	return 99
}

func Run(filename string) {
	file, err := os.Open(filename)

	if err != nil {
		fmt.Println("Error opening file:", err)
		return
	}

	scanner := bufio.NewScanner(file)
	scanner.Split(bufio.ScanLines)

	var total_score_base int = 0
	var total_score_extended int = 0

	for scanner.Scan() {
		line := scanner.Text()
		utf8 := utf8string.NewString(line)

		opponent := move(utf8.At(0))
		us := move(utf8.At(2))

		total_score_base += score(opponent, us)

		target := result(utf8.At(2))
		computed_move := compute_move(opponent, target)
		total_score_extended += score(opponent, computed_move)
	}

	file.Close()

	fmt.Println("Total initial score is", total_score_base)
	fmt.Println("Total score with back compute is", total_score_extended)
}