day17, dijkstra doesn't work

right? just because if found a shorter path, doesn't mean i don't need
to check other directions.
i have, because maybe they are not blocked and will provide better
solution.
so, yikes

day17/clumsyCrucible.go

@@ -0,0 +1,255 @@
+package day17
+
+import (
+	"fmt"
+	"log"
+	"math"
+	"os"
+	"strings"
+	// "time"
+)
+
+func Run() int {
+	fmt.Println("hello from day 17")
+	filename := "day17/example"
+	field := NewField(filename)
+	fmt.Printf("%+v\n", field)
+
+	field.RunDijkstra()
+
+	end := Coord{field.Height - 1, field.Width - 1}
+	lenToEnd := field.Paths[end].totalLength
+	fmt.Println("check visually:")
+	// fmt.Println(field.Paths[end].stringPathSoFar)
+	fmt.Println(field.printLastDirection())
+	return lenToEnd
+}
+
+// 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 {
+	totalLength     int
+	lastSteps       map[Direction]int
+	lastDirection   Direction
+	stringPathSoFar string
+	done            bool
+}
+
+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)
+	}
+
+	log.Printf("getting directions from %+v they are %+v", p, next)
+	return
+}
+
+type Field struct {
+	Paths         map[Coord]*PathSegmentEnd
+	Costs         [][]int
+	Height, Width int
+	Start         Coord
+}
+
+func NewField(filename string) Field {
+	enterCosts := ReadEnterCosts(filename)
+	startSegment := PathSegmentEnd{
+		totalLength:   0,
+		lastSteps:     make(map[Direction]int),
+		done:          true,
+		lastDirection: Downward, // fake, need to init direct neighbors also
+	}
+	initialPaths := make(map[Coord]*PathSegmentEnd)
+	initialPaths[Coord{0, 0}] = &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(from Coord, d Direction) (result PathSegmentEnd) {
+	curPath := f.Paths[from]
+	nextCoord := from.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{
+		totalLength:   newCost,
+		lastDirection: d,
+		lastSteps:     lastSteps,
+		stringPathSoFar: curPath.stringPathSoFar + d.AsSymbol(),
+	}
+}
+
+func (f *Field) RunDijkstra() {
+	checking := make(map[Coord]any, 0)
+
+	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"
+	}
+	return
+}
+

day17/example

@@ -0,0 +1,13 @@
+2413432311323
+3215453535623
+3255245654254
+3446585845452
+4546657867536
+1438598798454
+4457876987766
+3637877979653
+4654967986887
+4564679986453
+1224686865563
+2546548887735
+4322674655533

main.go

@@ -3,12 +3,12 @@ package main
 import (
 	"log"
 
-	"sunshine.industries/aoc2023/day16"
+	"sunshine.industries/aoc2023/day17"
 )
 
 func main() {
 	log.Print("> starting run:")
 
-	result := day16.Run()
-	log.Printf("\n\nday16 result: %d\n****\n", result)
+	result := day17.Run()
+	log.Printf("\n\nday17 result: %d\n****\n", result)
 }