Advent-of-Code-2023/day17/clumsyCrucible.go

package day17

import (
	"fmt"
	"log"
	"math"
	"os"
	"slices"
	"strings"
	// "time"
)

const ExampleResult string = ">>v>>>^>>>vv>>vv>vvv>vvv<vv>"

func Run() int {
	fmt.Println("hello from day 17")
	filename := "day17/example"
	field := NewField(filename)
	fmt.Printf("%+v\n", field)

	startSegment := PathSegmentEnd{
		endsAt:        Coord{0, 0},
		totalLength:   0,
		lastSteps:     make(map[Direction]int),
		done:          true,
		lastDirection: Downward, // fake, caution
	}

	end := Coord{field.Height - 1, field.Width - 1}
	field.runSearch(startSegment, end)

	pathsFoundToEnd := field.Paths[end]
	fmt.Println("check visually:")
	// fmt.Println(field.Paths[end].stringPathSoFar)
	minimal := math.MaxInt
	for _, path := range pathsFoundToEnd {
		fmt.Printf("%+v ; len is %d\n", path, path.totalLength)
		if path.totalLength < minimal {
			minimal = path.totalLength
		}
	}
	// fmt.Printf("i'm looking for %s\n", ExampleResult)
	return minimal
}

// let's do dijkstra. it also needs a priority queue

// priority queue would be over vertice. and would have to have enough information to
// calc the distance from neighbors.
// how to check condition of max 3 in one row?
// with each vertice store [horizontal:n|vertical:n] and if it's 3 just dont consider?

// so in iteration, i have some vertice, with horizontal:2 for example,
// i check all neighbors, if path through 'this' is shorter, set that as path,
// but also mark the path with len of straight.
//
// so priority queue is with 'path to next'
// or rather 'path to i,j'
// then check for neighbors (non finished), calc distance to them through this
// 	checking neighbors via 'path get directions' 'path get geighbors from directions'
// if shorter - update
// mark current as 'finished'
// so, i'll be checking cost to enter directly from this table,
// but check path len

func ReadEnterCosts(filename string) [][]int {
	bytes, err := os.ReadFile(filename)
	if err != nil {
		panic(fmt.Sprint("error reading file ", filename))
	}
	text := strings.TrimSpace(string(bytes))
	result := make([][]int, 0)
	for _, line := range strings.Split(text, "\n") {
		numbers := make([]int, 0)
		for _, digit := range line {
			num := int(digit - '0')
			numbers = append(numbers, num)
		}
		result = append(result, numbers)
	}
	return result
}

type Coord struct {
	Row, Col int
}

func (c Coord) applyDirection(d Direction) (result Coord) {
	result = c
	switch d {
	case Upward:
		result.Row -= 1
	case Downward:
		result.Row += 1
	case Leftward:
		result.Col -= 1
	case Rightward:
		result.Col += 1
	}
	return
}

type Direction int

const (
	Upward Direction = iota
	Downward
	Leftward
	Rightward
)

func (d Direction) String() string {
	strings := []string{"Up", "Down", "Left", "Right"}
	return strings[d]
}

func (d Direction) AsSymbol() string {
	strings := []string{"^", "v", "<", ">"}
	return strings[d]
}

func (d Direction) GetPerpendicular() (directions []Direction) {
	switch d {
	case Upward:
		directions = []Direction{Leftward, Rightward}
	case Downward:
		directions = []Direction{Leftward, Rightward}
	case Leftward:
		directions = []Direction{Upward, Downward}
	case Rightward:
		directions = []Direction{Upward, Downward}
	}
	return
}

type PathSegmentEnd struct {
	endsAt          Coord
	totalLength     int
	lastSteps       map[Direction]int
	lastDirection   Direction
	stringPathSoFar string
	done            bool
}

func (p *PathSegmentEnd) IsExamplePathPrefix() bool {
	return strings.HasPrefix(ExampleResult, p.stringPathSoFar)
}

func (p *PathSegmentEnd) NextDirections() (next []Direction) {
	next = append(next, p.lastDirection.GetPerpendicular()...)

	// last steps of 2 is max allowed 3 tiles in row
	lastSteps := p.lastSteps[p.lastDirection]
	if lastSteps < 3 {
		next = append(next, p.lastDirection)
	}

	// if p.IsExamplePathPrefix() {
	// 	log.Printf("getting directions from %+v they are %+v", p, next)
	// }
	// log.Printf("getting directions from %+v they are %+v", p, next)
	return
}

func (p *PathSegmentEnd) isDominating(other PathSegmentEnd) bool {
	if p.endsAt != other.endsAt {
		panic(fmt.Sprintf("comparing domination of paths on different ells: %+v %+v",
			p, other))
	}
	var thisDirection Direction
	var thisSteps int
	for thisDirection, thisSteps = range p.lastSteps {
		break
	}

	var otherDirection Direction
	var otherSteps int
	for otherDirection, otherSteps = range other.lastSteps {
		break
	}

	sameDirection := thisDirection == otherDirection
	// if other has less steps, then current total length is not important
	// other can still be more efficient in the future
	lessOrSameLastSteps := thisSteps <= otherSteps

	return sameDirection && lessOrSameLastSteps && p.totalLength < other.totalLength
}

type Field struct {
	Paths         map[Coord][]*PathSegmentEnd
	Costs         [][]int
	Height, Width int
	Start         Coord
}

func NewField(filename string) Field {
	enterCosts := ReadEnterCosts(filename)
	startSegment := PathSegmentEnd{
		endsAt:        Coord{0, 0},
		totalLength:   0,
		lastSteps:     make(map[Direction]int),
		done:          true,
		lastDirection: Downward, // fake, caution
	}
	initialPaths := make(map[Coord][]*PathSegmentEnd)
	initialPaths[Coord{0, 0}] = []*PathSegmentEnd{&startSegment}

	return Field{
		Paths:  initialPaths,
		Costs:  enterCosts,
		Height: len(enterCosts),
		Width:  len(enterCosts[0]),
		Start:  Coord{0, 0},
	}
}

func (f *Field) isValid(c Coord) bool {
	return c.Col >= 0 && c.Row >= 0 && c.Row < f.Height && c.Col < f.Width
}

// presupposes that direction is valid
func (f *Field) continuePathInDirection(curPath PathSegmentEnd, d Direction, finish Coord) (result PathSegmentEnd) {
	nextCoord := curPath.endsAt.applyDirection(d)
	moveCost := f.Costs[nextCoord.Row][nextCoord.Col]
	newCost := curPath.totalLength + moveCost
	lastSteps := make(map[Direction]int)

	curPathStepsIntoThisDirection, found := curPath.lastSteps[d]
	if !found {
		lastSteps[d] = 1
	} else {
		lastSteps[d] = curPathStepsIntoThisDirection + 1
	}

	return PathSegmentEnd{
		endsAt:          nextCoord,
		totalLength:     newCost,
		lastDirection:   d,
		lastSteps:       lastSteps,
		stringPathSoFar: curPath.stringPathSoFar + d.AsSymbol(),
		done: nextCoord == finish,
	}
}

func (f *Field) runSearch(curPath PathSegmentEnd, finish Coord) {

	// if len(curPath.stringPathSoFar) > f.Height+f.Width {
	// 	if curPath.IsExamplePathPrefix() {
	// 		log.Printf(">> CUTOFF %+v\n", curPath)
	// 	}
	// 	return
	// }
	// if start is also finish : this path is done
	// record the length, for the coord?
	// get directions,
	// if no directions : this path is done
	// get neighbords,
	// for each neighbor calc what whould be path if we went to the neighbor
	// if neighbor already known path which DOMINATES current - do not continue
	//
	// in the end for each vertice there will be map[direction][]PathSegmentEnd
	current := curPath.endsAt
	if current == finish {
		if curPath.IsExamplePathPrefix() {
			log.Printf(">> reached end with %+v\n", curPath)
		}
		return
	}
	directions := curPath.NextDirections()

	if len(directions) == 0 {
		return
	}

checkingNeighbors:
	for _, d := range directions {
		nextCoord := curPath.endsAt.applyDirection(d)
		if !f.isValid(nextCoord) {
			continue
		}
		ponentialPath := f.continuePathInDirection(curPath, d, finish)
		knownPathsToNeighbor := f.Paths[ponentialPath.endsAt]
		for _, knownPath := range knownPathsToNeighbor {
			if knownPath.isDominating(ponentialPath) {
				continue checkingNeighbors
			}
			// if our potential path is not dominated, then save as potential path
			// and would be nice to remove all known paths which are dominated by this potential
		}
		filteredKnownPaths := slices.DeleteFunc(knownPathsToNeighbor, func(previous *PathSegmentEnd) bool {
			return ponentialPath.isDominating(*previous)
		})
		filteredKnownPaths = append(filteredKnownPaths, &ponentialPath)
		f.Paths[ponentialPath.endsAt] = filteredKnownPaths

		f.runSearch(ponentialPath, finish)
	}
}