work

2024/go/day20/day20.go

@@ -52,14 +52,54 @@ func Part1(input string) int {
 	return dist
 }
 func Part2(input string) int {
+	const saves int = 100
+	count := 0
 	maze := Maze{}.Parse(input)
-	fmt.Println(maze)
+	//	fmt.Println(maze)
 	data := inputGraph(*maze)
 	graph := dijkstra.CreateGraph(data)
-	_, count := dijkstra.GetShortestPath(data.From, data.To, graph)
+	path, dist := dijkstra.GetShortestPath(data.From, data.To, graph)
+	cost := make(map[Vec]int)
+	cheats := []Cheat{}
+
+	for i, p := range path {
+		cost[Vec{p.X, p.Y}] = i
+	}
+	cheat_data := cheatGraph(*maze)
+
+	for _, s := range path[:len(path)-saves] {
+		fmt.Println("Checking start:", s)
+		for _, e := range path[saves:] {
+			fmt.Println("\tChecking end", e)
+			cheat_data_1 := cheatGraphAdd(maze, cheat_data, s)
+			cheat_data_2 := cheatGraphAdd(maze, cheat_data_1, e)
+			cheat_graph := dijkstra.CreateGraph(cheat_data_2)
+			_, cheat_dist := dijkstra.GetShortestPath(dijkstra.Point{X: s.X, Y: s.Y}, dijkstra.Point{X: e.X, Y: e.Y}, cheat_graph)
+			fmt.Println("\t\tcheat distance:", cheat_dist)
+			if cheat_dist <= 20 {
+				cheat := Cheat{start: Vec{s.X, s.Y}, end: Vec{e.X, e.Y}, cost: cost[Vec{s.X, s.Y}] + cheat_dist + dist - cost[Vec{e.X, e.Y}]}
+				fmt.Println("\t\tSaving cheat:", cheat)
+				cheats = append(cheats, cheat)
+			}
+		}
+	}
+	for _, cheat := range cheats {
+		save := dist - cheat.cost
+		//		fmt.Println("[", i, "]", "save", save)
+		if save >= saves {
+			count++
+		}
+	}
 	return count
 }
 
+func abs(in int) int {
+	if in < 0 {
+		return in * -1
+	}
+	return in
+}
+
 func inputGraph(maze Maze) dijkstra.InputGraph {
 	data := dijkstra.InputGraph{}
 	data.From = dijkstra.Point{X: maze.start.x, Y: maze.start.y}
@@ -89,6 +129,58 @@ func inputGraph(maze Maze) dijkstra.InputGraph {
 	return data
 }
 
+func cheatGraph(maze Maze) dijkstra.InputGraph {
+	data := dijkstra.InputGraph{}
+	for y := 0; y < maze.height; y++ {
+		for x := 0; x < maze.width; x++ {
+			if maze.grid.Get(x, y) == CORRIDOR {
+				continue
+			}
+			for _, dir := range DIRECTIONS {
+				nx, ny := x+dir.x, y+dir.y
+				if nx < 0 || ny < 0 || nx >= maze.width || ny >= maze.height {
+					continue
+				}
+				if maze.grid.Get(nx, ny) == CORRIDOR {
+					continue
+				}
+				data.Graph = append(data.Graph, dijkstra.InputData{
+					Source:      dijkstra.Point{X: x, Y: y},
+					Destination: dijkstra.Point{X: nx, Y: ny},
+					Weight:      1,
+				})
+			}
+		}
+	}
+
+	return data
+}
+
+func cheatGraphAdd(maze *Maze, in dijkstra.InputGraph, s dijkstra.Point) dijkstra.InputGraph {
+	x := s.X
+	y := s.Y
+	out := dijkstra.InputGraph{}
+	out.From = in.From
+	out.To = in.To
+	out.Graph = append([]dijkstra.InputData{}, in.Graph...)
+
+	for _, dir := range DIRECTIONS {
+		nx, ny := x+dir.x, y+dir.y
+		if nx < 0 || ny < 0 || nx >= maze.width || ny >= maze.height {
+			continue
+		}
+		if maze.grid.Get(nx, ny) == CORRIDOR {
+			continue
+		}
+		out.Graph = append(out.Graph, dijkstra.InputData{
+			Source:      dijkstra.Point{X: x, Y: y},
+			Destination: dijkstra.Point{X: nx, Y: ny},
+			Weight:      1,
+		})
+	}
+	return out
+}
+
 func (m Maze) Parse(input string) *Maze {
 	m.grid = inputs.ToGrid2D(input, "\n", "", '?', func(c string) Cell { return Cell(c[0]) })
 	m.height, m.width = m.grid.SizeY(), m.grid.SizeX()