2016-day17: md5 for bfs directions

2016/day17/main.go

@@ -0,0 +1,79 @@
+package main
+
+import (
+	"crypto/md5"
+	"flag"
+	"fmt"
+	"regexp"
+
+	"github.com/alexchao26/advent-of-code-go/cast"
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	ans := md5Bfs(util.ReadFile("./input.txt"), part)
+	fmt.Println("Output:", ans)
+}
+
+var openPattern = regexp.MustCompile("[b-f]")
+
+type node struct {
+	coords   [2]int
+	path     string
+	distance int
+}
+
+func md5Bfs(input string, part int) string {
+	queue := []node{{path: input}}
+	var longestPath string
+	for len(queue) > 0 {
+		front := queue[0]
+		queue = queue[1:]
+
+		if front.coords == [2]int{3, 3} {
+			validPath := front.path[len(input):]
+			if part == 1 {
+				return validPath
+			}
+
+			if len(longestPath) < len(validPath) {
+				longestPath = validPath
+			}
+			// cannot pass through the end point
+			continue
+		}
+
+		hash := fmt.Sprintf("%x", md5.Sum([]byte(front.path)))
+
+		for i, direction := range []struct {
+			char    string
+			rowDiff int
+			colDiff int
+		}{
+			{"U", -1, 0},
+			{"D", 1, 0},
+			{"L", 0, -1},
+			{"R", 0, 1},
+		} {
+			nextRow := front.coords[0] + direction.rowDiff
+			nextCol := front.coords[1] + direction.colDiff
+			if nextRow >= 0 && nextRow < 4 && nextCol >= 0 && nextCol < 4 {
+				if openPattern.MatchString(hash[i : i+1]) {
+					queue = append(queue, node{
+						coords:   [2]int{nextRow, nextCol},
+						path:     front.path + direction.char,
+						distance: front.distance + 1,
+					})
+				}
+			}
+		}
+	}
+
+	// part 2, stringified number...
+	return cast.ToString(len(longestPath))
+}

2016/day17/main_test.go

@@ -0,0 +1,28 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func Test_md5Bfs(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		part  int
+		want  string
+	}{
+		{"part1_example1", "ihgpwlah", 1, "DDRRRD"},
+		{"part1_actual", util.ReadFile("input.txt"), 1, "DDRUDLRRRD"},
+		{"part2_example1", "ihgpwlah", 2, "370"},
+		{"part2_actual", util.ReadFile("input.txt"), 2, "398"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := md5Bfs(tt.input, tt.part); got != tt.want {
+				t.Errorf("md5Bfs() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}