aoc-2018-day-09.go

package main

import (
	"bufio"
	"container/ring"
	"flag"
	"fmt"
	"os"
)

type Input struct {
	Line             string
	Players          int
	LastMarblePoints int
}

func readInput(filename string) []Input {
	fileHandle, _ := os.Open(filename)
	defer fileHandle.Close()
	fileScanner := bufio.NewScanner(fileHandle)

	inputList := []Input{}

	for fileScanner.Scan() {
		line := fileScanner.Text()
		if len(line) > 0 {
			i := Input{}
			i.Line = line

			fmt.Sscanf(line, "%d players; last marble is worth %d points", &i.Players, &i.LastMarblePoints)

			inputList = append(inputList, i)
		}
	}

	return inputList
}

var file = flag.String("file", "./input.txt", "file used for input")

func main() {
	flag.Parse()

	inputList := readInput(*file)

	play(inputList, 1)
	play(inputList, 100)
}

func play(inputList []Input, multiply int) {
	for _, input := range inputList {
		input.LastMarblePoints = input.LastMarblePoints * multiply

		r := ring.New(1)
		r.Value = 0

		scores := make(map[int]int, input.Players)
		curPlayer := 1

		for x := 1; x < input.LastMarblePoints; x++ {
			if x%23 == 0 {
				r = r.Move(-8)
				unl := r.Unlink(1)
				scores[curPlayer] += unl.Value.(int) + x
				r = r.Next()
			} else {
				nr := ring.New(1)
				nr.Value = x
				r = r.Move(1)
				r = r.Link(nr)
				r = r.Prev()
			}
			curPlayer ++
			if curPlayer > input.Players {
				curPlayer = 1
			}
		}

		highest := 0
		highestScoringPlayer := 0
		for pl, score := range scores {
			if score > highest {
				highest = score
				highestScoringPlayer = pl
			}
		}

		fmt.Printf("Last marble %d, curPlayer %d, high score %d\n", input.LastMarblePoints, highestScoringPlayer, highest)
	}
}