adventofcode/2024/day14/main.go

package main

import (
	"fmt"
	"math"

	h "git.bullercodeworks.com/brian/adventofcode/helpers"
)

func main() {
	inp := h.StdinToStringSlice()
	part1(inp)
	fmt.Println()
	part2(inp)
}

func part1(inp []string) {
	fmt.Println("# Part 1")
	// Main Input size
	sizeX, sizeY := 101, 103
	bots := parseInput(inp, sizeX, sizeY)
	for i := 0; i < 100; i++ {
		for j := range bots {
			bots[j].Move()
		}
	}
	for i := range bots {
		fmt.Println(bots[i])
	}
	qCnt := make([]int, 4)
	for y := 0; y < sizeY; y++ {
		for x := 0; x < sizeX; x++ {
			if x == sizeX/2 || y == sizeY/2 {
				fmt.Print(" ")
				continue
			}
			bCnt := 0
			for i := range bots {
				if x == bots[i].X && y == bots[i].Y {
					bCnt++
					if x < sizeX/2 {
						if y < sizeY/2 {
							qCnt[0]++
						} else {
							qCnt[2]++
						}
					} else {
						if y < sizeY/2 {
							qCnt[1]++
						} else {
							qCnt[3]++
						}
					}
				}
			}
			if bCnt > 0 {
				fmt.Print(bCnt)
			} else {
				fmt.Print(".")
			}
		}
		fmt.Println()
	}
	fmt.Println("Safety Factor:", (qCnt[0] * qCnt[1] * qCnt[2] * qCnt[3]))
}

func part2(inp []string) {
	fmt.Println("# Part 2")
	// Main Input size
	sizeX, sizeY := 101, 103
	bots := parseInput(inp, sizeX, sizeY)
	printState := func() {
		for y := 0; y < sizeY; y++ {
			for x := 0; x < sizeX; x++ {
				btCnt := 0
				for _, b := range bots {
					if b.X == x && b.Y == y {
						btCnt++
					}
				}
				if btCnt == 0 {
					fmt.Print(".")
				} else if btCnt < 10 {
					fmt.Print(btCnt)
				} else {
					fmt.Print("#")
				}
			}
			fmt.Println()
		}
	}
	// My hypothesis: most bots will be close to each other for the answer
	lowest := h.MAX_INT
	var lowStdX, lowStdY float64
	for steps := 0; steps < 10000000; steps++ {
		xs := make([]int, 0, len(bots))
		ys := make([]int, 0, len(bots))
		for j := range bots {
			bots[j].Move()
			xs = append(xs, bots[j].X)
			ys = append(ys, bots[j].Y)
		}
		// After finding it, I added this to print it out :D
		if steps == 7036 {
			printState()
		}
		wrkX, wrkY := stdev(xs), stdev(ys)
		if lowest == h.MAX_INT || (wrkX < lowStdX && wrkY < lowStdY) {
			fmt.Println(lowest, ":", lowStdX, lowStdY)
			lowStdX, lowStdY, lowest = wrkX, wrkY, steps
		}
	}
	fmt.Println("Steps to Easter Egg:", lowest)
}

func stdev(vals []int) float64 {
	m := 0.0
	for _, w := range vals {
		m += float64(w)
	}
	m /= float64(len(vals))
	v := 0.0
	for _, w := range vals {
		diff := float64(w) - m
		v += diff * diff
	}
	return math.Sqrt(v / float64(len(vals)))
}

var botRaw = "p=%d,%d v=%d,%d"

type Bot struct {
	X, Y, Vx, Vy int
	mX, mY       int
}

func NewBot(inp string) *Bot {
	b := Bot{}
	fmt.Sscanf(inp, botRaw, &b.X, &b.Y, &b.Vx, &b.Vy)
	return &b
}

func (b *Bot) Move() {
	b.X = (b.X + b.Vx + b.mX) % b.mX
	b.Y = (b.Y + b.Vy + b.mY) % b.mY
}

func (b *Bot) Overlaps(bt *Bot) bool {
	return b.X == bt.X && b.Y == bt.Y
}

func (b Bot) String() string {
	return fmt.Sprintf(botRaw, b.X, b.Y, b.Vx, b.Vy)
}

func parseInput(inp []string, mX, mY int) []*Bot {
	var ret []*Bot
	for i := range inp {
		b := NewBot(inp[i])
		b.mX, b.mY = mX, mY
		ret = append(ret, b)
	}
	return ret
}