advent-of-code/aoc2023/day21/main.go

package main

import (
	"bufio"
	_ "embed"
	"fmt"

	aoc "go.sour.is/advent-of-code"
)

// var log = aoc.Log

func main() { aoc.MustResult(aoc.Runner(runner(64))) }

type result struct {
	valuePT1 int
	valuePT2 int
}

func (r result) String() string { return fmt.Sprintf("%#v", r) }

func runner(rounds int) func(scan *bufio.Scanner) (*result, error) {
	return func(scan *bufio.Scanner) (*result, error) {
		var garden garden

		for scan.Scan() {
			txt := scan.Text()
			garden.m = append(garden.m, []rune(txt))

			for i, c := range txt {
				if c == 'S' {
					garden.start[0] = len(garden.m) - 1
					garden.start[1] = i
				}
			}
		}
		garden.Step(rounds)
		return &result{
			valuePT1: len(garden.steps[len(garden.steps)-1]),
		}, nil
	}
}

type garden struct {
	start aoc.Point[int]
	m     [][]rune
	steps []aoc.Set[aoc.Point[int]]
}

func (g *garden) Neighbors(p aoc.Point[int]) []aoc.Point[int] {
	var neighbors []aoc.Point[int]
	for _, n := range []aoc.Point[int]{
		{p[0] - 1, p[1]},
		{p[0] + 1, p[1]},
		{p[0], p[1] - 1},
		{p[0], p[1] + 1},
	} {
		if n[0] >= 0 && n[0] < len(g.m) && n[1] >= 0 && n[1] < len(g.m[0]) && g.m[n[0]][n[1]] != '#' {
			neighbors = append(neighbors, n)
		}
	}
	return neighbors
}

func (g *garden) Step(n int) {
	if len(g.steps) == 0 {
		g.steps = append(g.steps, aoc.NewSet(g.start))
	}

	for step := range(n) {
		g.steps = append(g.steps, aoc.NewSet[aoc.Point[int]]())
		for p := range g.steps[step] {
			for _, n := range g.Neighbors(p) {
				g.steps[step+1].Add(n)
			}
		}
	}
}

func (g garden) String() string {
	var b []rune
	for i, line := range g.m {
		if i == g.start[0] {
			line[g.start[1]] = 'X'
		}

		if steps := len(g.steps) - 1; steps > 0 {	
			for p := range g.steps[len(g.steps)-1] {
				if p[0] == i {
					line[p[1]] = 'O'
				}
			}
		}

		b = append(b, line...)
		b = append(b, '\n')
	}
	return string(b)
}