🌅

solutions/day12/day12.go

@@ -0,0 +1,174 @@
+package day12
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+)
+
+type Point struct {
+	x int
+	y int
+}
+
+func to_level(r rune) int {
+	return int(r - 'a')
+}
+
+func from_level(l int) rune {
+	return rune('a' + l)
+}
+
+func validMove(p1 Point, p2 Point, grid [][]int) bool {
+	if p2.x < 0 || p2.y < 0 || p2.x >= len(grid[0]) || p2.y >= len(grid) {
+		return false
+	}
+
+	diff := grid[p2.y][p2.x] - grid[p1.y][p1.x]
+	return (diff <= 1)
+}
+
+func updateDistances(grid [][]int, distances [][]int) bool {
+	y := 0
+	updatedSomething := false
+
+	for _, row := range distances {
+		for x := range row {
+			best := distances[y][x]
+			nexts := nextSteps(Point{x, y}, grid)
+
+			for _, next := range nexts {
+				if distances[next.y][next.x] != -1 {
+					if best == -1 || distances[next.y][next.x]+1 < best {
+						fmt.Println("Found a live one; at", Point{x, y}, "with score", distances[y][x], "going to", next, "with score", distances[next.y][next.x])
+						best = distances[next.y][next.x] + 1
+						updatedSomething = true
+					}
+				}
+			}
+
+			distances[y][x] = best
+		}
+		y += 1
+	}
+
+	return updatedSomething
+}
+
+func nextSteps(p Point, grid [][]int) []Point {
+	retval := []Point{}
+
+	// point above
+	above := Point{p.x, p.y - 1}
+	if validMove(p, above, grid) {
+		retval = append(retval, above)
+	}
+	// point below
+	below := Point{p.x, p.y + 1}
+	if validMove(p, below, grid) {
+		retval = append(retval, below)
+	}
+	// point left
+	left := Point{p.x - 1, p.y}
+	if validMove(p, left, grid) {
+		retval = append(retval, left)
+	}
+	// point right
+	right := Point{p.x + 1, p.y}
+	if validMove(p, right, grid) {
+		retval = append(retval, right)
+	}
+
+	return retval
+}
+
+func printMap(grid [][]int) {
+	for _, line := range grid {
+		for _, v := range line {
+			fmt.Printf("%c", from_level(v))
+		}
+		fmt.Println()
+	}
+}
+
+func printDistances(grid [][]int, distances [][]int) {
+	for y, line := range distances {
+		for x, v := range line {
+			fmt.Printf("%5d/%c", v, from_level(grid[y][x]))
+		}
+		fmt.Println()
+	}
+}
+
+func Run(filename string) {
+	file, err := os.Open(filename)
+
+	if err != nil {
+		fmt.Println("Error opening file:", err)
+		return
+	}
+
+	scanner := bufio.NewScanner(file)
+	scanner.Split(bufio.ScanLines)
+	grid := [][]int{}
+	distances := [][]int{}
+	var start Point
+	var end Point
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		row := []int{}
+		drow := []int{}
+
+		y := len(grid)
+		for x, r := range []rune(line) {
+			if r == 'S' {
+				r = 'a'
+				start = Point{x, y}
+			}
+			if r == 'E' {
+				r = 'z'
+				end = Point{x, y}
+			}
+			row = append(row, to_level(r))
+			drow = append(drow, -1)
+		}
+		grid = append(grid, row)
+		distances = append(distances, drow)
+	}
+
+	file.Close()
+
+	distances[end.y][end.x] = 0
+
+	printMap(grid)
+	printDistances(grid, distances)
+	fmt.Printf("Start position is (%d, %d)\n", start.x, start.y)
+	fmt.Printf("End position is (%d, %d)\n", end.x, end.y)
+	fmt.Println("Valid first steps:", nextSteps(start, grid))
+	iteration := 0
+	keepGoing := true
+	for keepGoing {
+		fmt.Println("Running iteration", iteration)
+		printDistances(grid, distances)
+		keepGoing = updateDistances(grid, distances)
+		iteration += 1
+	}
+	fmt.Printf("Best path is %d steps long.\n", distances[start.y][start.x])
+
+	closestAIs := -1
+	for y, line := range grid {
+		for x, v := range line {
+			if from_level(v) == 'a' {
+				distance := distances[y][x]
+				fmt.Printf("Point (%d, %d) is level `a`, and is %d steps from end.\n", x, y, distance)
+				if distance != -1 {
+					if closestAIs == -1 || distance < closestAIs {
+						closestAIs = distance
+					}
+				}
+			}
+		}
+	}
+	fmt.Println("The closest 'a' is", closestAIs, "steps away.")
+}