day17, example

day17/clumsyCrucible.go

@@ -5,24 +5,42 @@ import (
 	"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)
 
-	field.RunDijkstra()
+	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}
-	lenToEnd := field.Paths[end].totalLength
+	field.runSearch(startSegment, end)
+
+	pathsFoundToEnd := field.Paths[end]
 	fmt.Println("check visually:")
 	// fmt.Println(field.Paths[end].stringPathSoFar)
-	fmt.Println(field.printLastDirection())
-	return lenToEnd
+	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
@@ -116,6 +134,7 @@ func (d Direction) GetPerpendicular() (directions []Direction) {
 }
 
 type PathSegmentEnd struct {
+	endsAt          Coord
 	totalLength     int
 	lastSteps       map[Direction]int
 	lastDirection   Direction
@@ -123,6 +142,10 @@ type PathSegmentEnd struct {
 	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()...)
 
@@ -132,12 +155,40 @@ func (p *PathSegmentEnd) NextDirections() (next []Direction) {
 		next = append(next, p.lastDirection)
 	}
 
-	log.Printf("getting directions from %+v they are %+v", p, next)
+	// 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
+	Paths         map[Coord][]*PathSegmentEnd
 	Costs         [][]int
 	Height, Width int
 	Start         Coord
@@ -146,13 +197,14 @@ type Field struct {
 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, need to init direct neighbors also
+		lastDirection: Downward, // fake, caution
 	}
-	initialPaths := make(map[Coord]*PathSegmentEnd)
-	initialPaths[Coord{0, 0}] = &startSegment
+	initialPaths := make(map[Coord][]*PathSegmentEnd)
+	initialPaths[Coord{0, 0}] = []*PathSegmentEnd{&startSegment}
 
 	return Field{
 		Paths:  initialPaths,
@@ -168,9 +220,8 @@ func (f *Field) isValid(c Coord) bool {
 }
 
 // presupposes that direction is valid
-func (f *Field) continuePathInDirection(from Coord, d Direction) (result PathSegmentEnd) {
-	curPath := f.Paths[from]
-	nextCoord := from.applyDirection(d)
+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)
@@ -183,73 +234,66 @@ func (f *Field) continuePathInDirection(from Coord, d Direction) (result PathSeg
 	}
 
 	return PathSegmentEnd{
+		endsAt:          nextCoord,
 		totalLength:     newCost,
 		lastDirection:   d,
 		lastSteps:       lastSteps,
 		stringPathSoFar: curPath.stringPathSoFar + d.AsSymbol(),
+		done: nextCoord == finish,
 	}
 }
 
-func (f *Field) RunDijkstra() {
-	checking := make(map[Coord]any, 0)
+func (f *Field) runSearch(curPath PathSegmentEnd, finish Coord) {
 
-	checking[f.Start] = struct{}{}
-
-	for len(checking) > 0 {
-		var currentCoord Coord
-		for key := range checking {
-			currentCoord = key
-			break
-		}
-		currentPath := f.Paths[currentCoord]
-		directions := currentPath.NextDirections()
-
-		for _, direction := range directions {
-			log.Printf("from %+v will examine in direction %s", currentCoord, direction)
-			neighborCoord := currentCoord.applyDirection(direction)
-			if !f.isValid(neighborCoord) {
-				continue // prevent going off the grid
-			}
-			neighborPathSoFar, found := f.Paths[neighborCoord]
-			if !found {
-				neighborPathSoFar = &PathSegmentEnd{
-					totalLength: math.MaxInt,
-				}
-				f.Paths[neighborCoord] = neighborPathSoFar
-			}
-
-			// log.Printf("about to check done on neighbor %+v\n", neighborPathSoFar)
-			if neighborPathSoFar.done {
-				continue // already found optimal
-			}
-
-			pathIfWeGoFromCurrent := f.continuePathInDirection(currentCoord, direction)
-			if pathIfWeGoFromCurrent.totalLength < neighborPathSoFar.totalLength {
-				f.Paths[neighborCoord] = &pathIfWeGoFromCurrent
-			}
-			checking[neighborCoord] = struct{}{}
-		}
-		f.Paths[currentCoord].done = true
-		delete(checking, currentCoord)
-
-		// fmt.Print(f.printLastDirection())
-		// time.Sleep(time.Second)
-	}
-}
-
-func (f *Field) printLastDirection() (result string) {
-	result += "\n"
-	for rowNum := 0; rowNum < f.Height; rowNum++ {
-		for colNum := 0; colNum < f.Width; colNum++ {
-			path, found := f.Paths[Coord{rowNum, colNum}]
-			if !found {
-				result += "."
-			} else {
-				result += path.lastDirection.AsSymbol()
-			}
-		}
-		result += "\n"
+	// 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)
+	}
+}