2018 day 9 - circular linked list

2018/day09/main.go

@@ -0,0 +1,93 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"strconv"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	if part == 1 {
+		ans := part1(util.ReadFile("./input.txt"))
+		fmt.Println("Output:", ans)
+	} else {
+		ans := part2(util.ReadFile("./input.txt"))
+		fmt.Println("Output:", ans)
+	}
+}
+
+func part1(input string) int {
+	players, lastPoints := parseInput(input)
+
+	currentMarble := &CircularLinkedListNode{nil, nil, 0}
+	currentMarble.left = currentMarble
+	currentMarble.right = currentMarble
+
+	playerTurn := 0
+	playerScores := make([]int, players)
+
+	for points := 1; points <= lastPoints; points++ {
+		if points%23 == 0 {
+			for i := 0; i < 7; i++ {
+				currentMarble = currentMarble.left
+			}
+
+			playerScores[playerTurn] += points
+			playerScores[playerTurn] += currentMarble.val
+			currentMarble = currentMarble.RemoveSelf()
+		} else {
+			currentMarble = currentMarble.right
+			currentMarble.AddToRight(points)
+			currentMarble = currentMarble.right
+		}
+
+		playerTurn++
+		playerTurn %= players
+	}
+
+	return util.MaxInts(playerScores...)
+}
+
+func part2(input string) int {
+	// lazily modify input...
+	split := strings.Split(input, " ")
+	steps := util.StrToInt(split[6]) * 100
+	split[6] = strconv.Itoa(steps)
+
+	return part1(strings.Join(split, " "))
+}
+
+func parseInput(input string) (players int, lastPoints int) {
+	split := strings.Split(input, " ")
+	return util.StrToInt(split[0]), util.StrToInt(split[6])
+}
+
+type CircularLinkedListNode struct {
+	left, right *CircularLinkedListNode
+	val         int
+}
+
+func (c *CircularLinkedListNode) AddToRight(val int) {
+	newNode := CircularLinkedListNode{
+		left:  c,
+		right: c.right,
+		val:   val,
+	}
+	c.right.left = &newNode
+	c.right = &newNode
+}
+
+func (c *CircularLinkedListNode) RemoveSelf() *CircularLinkedListNode {
+	// not handling edge case of < 2 nodes because it's not going to get hit in this case
+	c.left.right = c.right
+	c.right.left = c.left
+	return c.right
+}