2024 day17 - oof clusmy cart was tough

2023/day17/main.go

@@ -0,0 +1,153 @@
+package main
+
+import (
+	_ "embed"
+	"flag"
+	"fmt"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/cast"
+	"github.com/alexchao26/advent-of-code-go/data-structures/heap"
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+//go:embed input.txt
+var input string
+
+func init() {
+	// do this in init (not main) so test file has same input
+	input = strings.TrimRight(input, "\n")
+	if len(input) == 0 {
+		panic("empty input.txt file")
+	}
+}
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	if part == 1 {
+		ans := clumsyCart(input, 1, 3)
+		util.CopyToClipboard(fmt.Sprintf("%v", ans))
+		fmt.Println("Output:", ans)
+	} else {
+		ans := clumsyCart(input, 4, 10)
+		util.CopyToClipboard(fmt.Sprintf("%v", ans))
+		fmt.Println("Output:", ans)
+	}
+}
+
+func clumsyCart(input string, minMoves, maxMoves int) int {
+	grid := parseInput(input)
+
+	minHeap := heap.NewMinHeap()
+	minHeap.Add(bfsNode{
+		heatLoss:  0,
+		row:       0,
+		col:       0,
+		lastDir:   right,
+		debugPath: "",
+	})
+	minHeap.Add(bfsNode{
+		heatLoss:  0,
+		row:       0,
+		col:       0,
+		lastDir:   down,
+		debugPath: "",
+	})
+
+	// store lowest heat loss for each coordinate for each direction, slightly suboptimal
+	// because it can be divided into vertical and horizontal
+	// instead of L, R, U, D. But it's a constant time optimization but it runs fast enough
+	cache := map[string]int{}
+
+	for minHeap.Length() > 0 {
+		node := minHeap.Remove().(bfsNode)
+
+		key := fmt.Sprintf("%d %d - %v", node.row, node.col, node.lastDir)
+		if val, ok := cache[key]; ok {
+			if node.heatLoss >= val {
+				// exit if the current heatLoss isn't better
+				continue
+			} else {
+				cache[key] = node.heatLoss
+			}
+		} else {
+			cache[key] = node.heatLoss
+		}
+
+		if node.row == len(grid)-1 && node.col == len(grid[0])-1 {
+			return node.heatLoss
+		}
+
+		// just add a node for each vertical direction, then those will move vertically as well
+		// which covers all possibilities
+		for _, nextDir := range verticalTurns[node.lastDir] {
+			summedHeatLoss := 0
+			for i := 1; i <= maxMoves; i++ {
+				nextRow := node.row + nextDir[0]*i
+				nextCol := node.col + nextDir[1]*i
+
+				// skip if out of range
+				if nextRow < 0 || nextRow >= len(grid) || nextCol < 0 || nextCol >= len(grid[0]) {
+					continue
+				}
+
+				summedHeatLoss += grid[nextRow][nextCol]
+
+				// do not add to heap if the cart has moved less than the minimum required moves (part 2)
+				if i < minMoves {
+					continue
+				}
+
+				minHeap.Add(bfsNode{
+					heatLoss:  node.heatLoss + summedHeatLoss,
+					row:       nextRow,
+					col:       nextCol,
+					lastDir:   nextDir,
+					debugPath: node.debugPath + fmt.Sprintf("%d,%d ", nextRow, nextCol),
+				})
+			}
+		}
+	}
+
+	panic("should return from heap processing")
+}
+
+type bfsNode struct {
+	heatLoss  int
+	row, col  int
+	lastDir   direction
+	debugPath string
+}
+
+func (b bfsNode) Value() int {
+	return b.heatLoss
+}
+
+type direction [2]int
+
+var up = direction{-1, 0}
+var down = direction{1, 0}
+var left = direction{0, -1}
+var right = direction{0, 1}
+
+var verticalTurns = map[direction][2]direction{
+	up:    {left, right},
+	down:  {left, right},
+	left:  {up, down},
+	right: {up, down},
+}
+
+func parseInput(input string) (ans [][]int) {
+	for _, line := range strings.Split(input, "\n") {
+		row := []int{}
+		for _, str := range strings.Split(line, "") {
+			row = append(row, cast.ToInt(str))
+		}
+		ans = append(ans, row)
+	}
+	return ans
+}

2023/day17/main_test.go

@@ -0,0 +1,65 @@
+package main
+
+import (
+	"testing"
+)
+
+var example = `2413432311323
+3215453535623
+3255245654254
+3446585845452
+4546657867536
+1438598798454
+4457876987766
+3637877979653
+4654967986887
+4564679986453
+1224686865563
+2546548887735
+4322674655533`
+
+func Test_clumsyCart(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		minMoves int
+		maxMoves int
+		want     int
+	}{
+		{
+			name:     "example",
+			input:    example,
+			minMoves: 1,
+			maxMoves: 3,
+			want:     102,
+		},
+		{
+			name:     "actual",
+			input:    input,
+			minMoves: 1,
+			maxMoves: 3,
+			want:     1001,
+		},
+		{
+			name:     "example_part2",
+			input:    example,
+			minMoves: 4,
+			maxMoves: 10,
+			want:     94,
+		},
+		{
+			name:     "actual",
+			input:    input,
+			minMoves: 1,
+			maxMoves: 3,
+			want:     1197,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := clumsyCart(tt.input, tt.minMoves, tt.maxMoves); got != tt.want {
+				t.Errorf("clumsyCart() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}