day20

2024/go/day20/day20.go

@@ -4,7 +4,6 @@ import (
 	"adventofcode2024/utils/dijkstra"
 	"adventofcode2024/utils/grid2d"
 	"adventofcode2024/utils/inputs"
-	"fmt"
 )
 
 type (
@@ -21,6 +20,11 @@ type (
 		end           Vec
 		grid          *grid2d.Grid[Cell]
 	}
+	Cheat struct {
+		start Vec
+		end   Vec
+		cost  int
+	}
 )
 
 const (
@@ -40,24 +44,47 @@ var (
 )
 
 func Part1(input string) int {
+	count := 0
 	maze := Maze{}.Parse(input)
-	fmt.Println(maze)
+	//	fmt.Println(maze)
 	data := inputGraph(*maze)
 	graph := dijkstra.CreateGraph(data)
 	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
+	}
 	for _, p := range path {
 		maze.grid.Set(p.X, p.Y, PATH)
+		for _, dir := range DIRECTIONS {
+			nx1, ny1 := p.X+dir.x, p.Y+dir.y
+			if maze.grid.Get(nx1, ny1) == WALL {
+				nx2, ny2 := p.X+dir.x+dir.x, p.Y+dir.y+dir.y
+				switch maze.grid.Get(nx2, ny2) {
+				case CORRIDOR:
+					if cost[Vec{p.X, p.Y}]+2 < cost[Vec{nx2, ny2}] {
+						cheats = append(cheats, Cheat{start: Vec{p.X, p.Y}, end: Vec{nx2, ny2}, cost: dist - cost[Vec{nx2, ny2}] + cost[Vec{p.X, p.Y}] + 2})
+					}
+				default:
+					break
+				}
+			}
+		}
 	}
-	fmt.Println(maze)
+	//	fmt.Println(maze)
-	return dist
+	for _, cheat := range cheats {
+		save := dist - cheat.cost
+		//		fmt.Println("[", i, "]", "save", save)
+		if save >= 100 {
+			count++
+		}
+	}
+	return count
 }
 func Part2(input string) int {
-	maze := Maze{}.Parse(input)
+	return 0
-	fmt.Println(maze)
-	data := inputGraph(*maze)
-	graph := dijkstra.CreateGraph(data)
-	_, count := dijkstra.GetShortestPath(data.From, data.To, graph)
-	return count
 }
 
 func inputGraph(maze Maze) dijkstra.InputGraph {

2024/go/main.go

@@ -26,6 +26,7 @@ import (
 	"adventofcode2024/day17"
 	"adventofcode2024/day18"
 	"adventofcode2024/day19"
+	"adventofcode2024/day20"
 	"adventofcode2024/utils"
 )
 
@@ -90,6 +91,9 @@ func main() {
 	case 19:
 		fmt.Printf("part 1: %d\n", day19.Part1(utils.Readfile(d)))
 		fmt.Printf("part 2: %d\n", day19.Part2(utils.Readfile(d)))
+	case 20:
+		fmt.Printf("part 1: %d\n", day20.Part1(utils.Readfile(d)))
+		fmt.Printf("part 2: %d\n", day20.Part2(utils.Readfile(d)))
 	default:
 		panic(fmt.Errorf("no such day: %d", d))
 	}