adventofcode/2023/day21/main.go

package main

import (
	"fmt"

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

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

func part1(input []string) {
	m := h.StringSliceToCoordByteMap(input)
	start, _ := m.FindFirst('S')
	m.Put(start, '.')
	result := []h.Coordinate{start}
	for i := 0; i < 64; i++ {
		result = findNext(&m, result)
	}
	fmt.Println("# Part 1")
	fmt.Println(len(result))
}

// 253370351984188 is too low
func part2(input []string) {
	m := h.StringSliceToCoordByteMap(input)
	start, _ := m.FindFirst('S')
	m.Put(start, '.')
	steps := 26501365
	p := make([]int, 3)
	size := len(input)
	half := size / 2
	fmt.Println("Getting Plots: p[0]")
	p[0], _ = getPlots(&m, half, 5)
	fmt.Println("Getting Plots: p[1]")
	m = h.StringSliceToCoordByteMap(input)
	p[1], _ = getPlots(&m, half+size, 5)
	fmt.Println("Getting Plots: p[2]")
	m = h.StringSliceToCoordByteMap(input)
	p[2], _ = getPlots(&m, half+2*size, 5)
	a := (p[2] + p[0] - 2*p[1]) / 2
	b := p[1] - p[0] - a
	c := p[0]
	n := steps / size
	result := a*n*n + b*n + c

	fmt.Println("# Part 2")
	fmt.Println(result)
}

var visited map[string]bool

func getPlots(m *h.CoordByteMap, steps int, factor int) (int, error) {
	sx, sy := m.ColCount(), m.RowCount()
	l := sy
	expandMap(m, factor)
	sx = l * (factor / 2)
	sy = l * (factor / 2)
	visited = make(map[string]bool)
	return len(nextStep(sx, sy, 0, steps, m)), nil
}

func isPlot(m *h.CoordByteMap, x, y int) bool {
	return m.Get(h.Coordinate{X: x, Y: y}) == '.'
}
func nextStep(x, y, step, max int, m *h.CoordByteMap) []h.Coordinate {
	var acc []h.Coordinate
	var key = fmt.Sprintf("%d;%d;%d", x, y, step)
	if _, ok := visited[key]; ok {
		return []h.Coordinate{}
	} else {
		visited[key] = true
	}
	if step == max {
		return []h.Coordinate{{X: x, Y: y}}
	}
	if x > 0 && isPlot(m, x-1, y) {
		acc = append(acc, nextStep(x-1, y, step+1, max, m)...)
	}
	if x < m.ColCount() && isPlot(m, x+1, y) {
		acc = append(acc, nextStep(x, y-1, step+1, max, m)...)
	}
	if y > 0 && isPlot(m, x, y-1) {
		acc = append(acc, nextStep(x, y-1, step+1, max, m)...)
	}
	if y < m.RowCount() && isPlot(m, x, y+1) {
		acc = append(acc, nextStep(x, y+1, step+1, max, m)...)
	}
	return acc
}

func expandMap(m *h.CoordByteMap, factor int) {
	stx, edx := m.TLX, m.BRX
	for f := 1; f < factor; f++ {
		for x := stx; x <= edx; x++ {
			col := m.GetCol(x)
			m.AddCol(col)
		}
		sty, edy := m.TLY, m.BRY
		for y := sty; y <= edy; y++ {
			row := m.GetRow(y)
			m.AddRow(row)
		}
	}
}

func part2BruteForce(input []string) {
	// Brute force just isn't going to cut it...
	m := h.StringSliceToCoordByteMap(input)
	m.StringEmptyIsSpace = true
	m.StringEmptyByte = '.'
	seen := make(map[h.Coordinate]bool)
	start, _ := m.FindFirst('S')
	m.Put(start, '.')
	result := []h.Coordinate{start}
	steps := 26501365
	for i := 0; i < steps; i++ {
		fmt.Println(h.CLEAR_SCREEN)
		fmt.Printf("%d/%d (%f)\n", i, steps, float64(i)/float64(steps))
		seen, result = findNextInfiniteRepeat(&m, seen, result)
		if i == 100 {
			break
		}
	}
	fmt.Println("# Part 2")
	fmt.Println(len(result))
	for i := range result {
		m.Put(result[i], 'O')
	}
	fmt.Println(m)
	// It's making a diamond shape...
}

func findNext(m *h.CoordByteMap, curr []h.Coordinate) []h.Coordinate {
	var result []h.Coordinate
	for _, c := range curr {
		for _, tst := range []h.Coordinate{
			c.North(), c.East(), c.South(), c.West(),
		} {
			if m.ContainsCoord(tst) && m.Get(tst) == '.' {
				var contains bool
				for i := range result {
					if result[i].Equals(tst) {
						contains = true
						break
					}
				}
				if !contains {
					result = append(result, tst)
				}
			}
		}
	}
	return result
}

func findNextInfiniteRepeat(m *h.CoordByteMap, seen map[h.Coordinate]bool, curr []h.Coordinate) (map[h.Coordinate]bool, []h.Coordinate) {
	var result []h.Coordinate
	for _, c := range curr {
		for _, tst := range []h.Coordinate{
			c.North(), c.East(), c.South(), c.West(),
		} {
			if seen[tst] {
				continue
			}
			wrkX, wrkY := tst.X, tst.Y
			for wrkX < m.TLX {
				wrkX += m.BRX
			}
			for wrkY < m.TLY {
				wrkY += m.BRY
			}
			wrk := h.Coordinate{X: (wrkX % m.BRX), Y: (wrkY % m.BRY)}
			if m.Get(wrk) == '.' {
				var contains bool
				for i := range result {
					if result[i].Equals(tst) {
						contains = true
						break
					}
				}
				if !contains {
					result = append(result, tst)
					seen[tst] = true
				}
			}
		}
	}
	return seen, result
}