day23: started hardcode of part2, way too slow

day23/aLongWalk.go

@@ -7,7 +7,7 @@ import (
 // length of longest scenic route
 func Run() int {
 	fmt.Println("day 23")
-	filename := "day23/example"
+	filename := "day23/input"
 	field := ReadField(filename)
 	finalPaths := RunAllScenicPaths(field)
 

day23/field.go

@@ -27,6 +27,35 @@ type Field struct {
 	StartCol, EndCol int
 }
 
+func (f *Field) NeighborsPart2(c Coord) (neighbors []Coord) {
+	symb, exists := f.Cells[c]
+	if !exists {
+		panic(fmt.Sprintf("coord %+v not found in field", c))
+	}
+
+	var coords []Coord
+	switch symb {
+	case Tree:
+		panic(fmt.Sprintf("attempting to get neighbors of a tree at %+v", c))
+	default:
+		coords = []Coord{
+			{Row: c.Row + 1, Col: c.Col},
+			{Row: c.Row - 1, Col: c.Col},
+			{Row: c.Row, Col: c.Col + 1},
+			{Row: c.Row, Col: c.Col - 1},
+		}
+	}
+
+	for _, coord := range coords {
+		neighborSymb, found := f.Cells[coord]
+		if !found || neighborSymb == Tree {
+			continue
+		}
+		neighbors = append(neighbors, coord)
+	}
+	return
+}
+
 func (f *Field) Neighbors(c Coord) (neighbors []Coord) {
 	symb, exists := f.Cells[c]
 	if !exists {

day23/notes.org

@@ -0,0 +1,67 @@
+#+title: Notes
+* ok, second part is long.
+and here optimization of storing direction of enter into path, and it's length,
+would that be helpful?
+it might not, because based on visited some future longer path might not be available.
+
+i don't know how to optimize.
+
+i could maybe do same calculation in parallel, somehow
+put not into queue, but into channel
+* wait a second. previous answer was 2018
+and now long checks result in me waiting for intermediate 1882.
+let's add early cutoffs, if not end by 2018, then abandon
+doubt that's implementable
+
+* well. do i want to try parallel?
+seems like false path, really
+like there should be a better optimizaiton first
+* maybe we could join detours into 'potential longest paths'
+like if we traverse, and get to a point which was previously visited,
+for evey path that went through that split path,
+i could check whether i can take paths that went through this point, and switch their part with the detoured part.
+* and maybe we could continue longest paths first?
+like making pathsToFurther a heap by visited.Cordinality ?
+
+oh, and then we'll find 'some path to end'
+and additional paths will try to add their detour.
+
+so, i guess when finding a path to end, i could save path to end for each point.
+then if i reach the point, i could check if i can use some of the
+
+and i guess if i do depth first then i'll always have all paths to end from a point if i return to it?
+* this sounds like an idea.
+with heap do depth first.
+
+if it's first visit to a point, just go further
+if i find the end, i'd want to mark all points on the path with path info
+
+hm. recursive calls might make this easier.
+because i'd want both 'prefixVisited' set and totalPathSet
+
+due to depth first, we'll discover shortest path first.
+and points will get mapped with this first (of potential multiple) path info to end.
+
+now if on followup steps i get into the point with info on paths to end,
+that should mean that i've already found all paths to end from that point, right?
+
+now i need to check for the 'detour' which 'paths to end' are still possible with that detour added
+by taking set of elements from this point, to end. and checking that intersection with detour elements is 0.
+
+if there are like this - report finding a new path, and save to all elements of that path somehow.
+
+and now on finding detours i wouldn't need to re-check path to end, that should save a lot of time
+** so how to go about in coding this?
+have shared map[Coord][]EndPathInfo
+
+the DFS means i'm recursing into each child.
+and taking the result of the call.
+it should be info on path to end? or multiple paths to end.
+which should be added to current node.
+
+and then calling with start point will return paths to end from start, and i'll be able to take the by length
+
+ok. but. if i'm entering the coord, and there are already paths to end.
+then i need to presume that those are only possible paths to end from this point,
+because all other paths should have been explored by now,
+i for my 'detour' determine whether it is consistent with any of already found paths to end.

day23/paths.go

@@ -1,6 +1,8 @@
 package day23
 
 import (
+	"log"
+
 	mapset "github.com/deckarep/golang-set/v2"
 )
 
@@ -10,7 +12,7 @@ type PathEnd struct {
 }
 
 func ExtendPath(p PathEnd, f Field) (nextPaths []PathEnd) {
-	endPointNeighbors := f.Neighbors(p.end)
+	endPointNeighbors := f.NeighborsPart2(p.end)
 	for _, potentialNewEnd := range endPointNeighbors {
 		if !p.visited.Contains(potentialNewEnd) {
 			nextVisited := p.visited.Clone()
@@ -39,6 +41,7 @@ func RunAllScenicPaths(f Field) (result []PathEnd) {
 
 		if curCheckedPath.end == theEndCoord {
 			result = append(result, curCheckedPath)
+			log.Printf("found end path of len %d . %+v", curCheckedPath.visited.Cardinality(), curCheckedPath)
 			continue
 		}