Day 17 Complete

2016/day17/main.go

@@ -0,0 +1,111 @@
+package main
+
+import (
+	"crypto/md5"
+	"fmt"
+	"os"
+
+	"../../"
+)
+
+var gridWidth, gridHeight int
+
+func main() {
+	var passcode string
+	gridWidth, gridHeight = 4, 4
+
+	if len(os.Args) < 2 {
+		printUsageAndExit()
+	}
+	passcode = os.Args[1]
+	if len(os.Args) >= 4 {
+		gridWidth = aoc.Atoi(os.Args[2])
+		gridHeight = aoc.Atoi(os.Args[3])
+	}
+	foundPaths := findPaths("", passcode)
+	if len(foundPaths) == 0 {
+		fmt.Println("Couldn't find a valid path!")
+		os.Exit(1)
+	}
+	shortestPath := foundPaths[0]
+	longestPath := foundPaths[0]
+	for i := range foundPaths {
+		if len(foundPaths[i]) < len(shortestPath) {
+			shortestPath = foundPaths[i]
+		}
+		if len(foundPaths[i]) > len(longestPath) {
+			longestPath = foundPaths[i]
+		}
+	}
+	fmt.Println("Shortest Path:", shortestPath)
+	fmt.Println("Longest Path Length:", len(longestPath))
+}
+
+func findPaths(path, passcode string) []string {
+	var ret []string
+	cX, cY := currPos(path)
+	if cY == gridHeight-1 && cX == gridWidth-1 {
+		return []string{path}
+	}
+	if cY > 0 && doorIsOpen(path, passcode, 'U') {
+		ret = append(ret, findPaths(path+"U", passcode)...)
+	}
+	if cY < (gridHeight-1) && doorIsOpen(path, passcode, 'D') {
+		ret = append(ret, findPaths(path+"D", passcode)...)
+	}
+	if cX > 0 && doorIsOpen(path, passcode, 'L') {
+		ret = append(ret, findPaths(path+"L", passcode)...)
+	}
+	if cX < (gridWidth-1) && doorIsOpen(path, passcode, 'R') {
+		ret = append(ret, findPaths(path+"R", passcode)...)
+	}
+	return ret
+}
+
+// We cache the last hash calculated
+// It should speed things up a little
+var lastHashInput string
+var lastHash string
+
+func doorIsOpen(path, passcode string, dir rune) bool {
+	if lastHashInput != passcode+path {
+		lastHashInput = passcode + path
+		lastHash = fmt.Sprintf("%x", md5.Sum([]byte(lastHashInput)))
+	}
+	switch dir {
+	case 'U':
+		return lastHash[0] >= 'b' && lastHash[0] <= 'f'
+	case 'D':
+		return lastHash[1] >= 'b' && lastHash[1] <= 'f'
+	case 'L':
+		return lastHash[2] >= 'b' && lastHash[2] <= 'f'
+	case 'R':
+		return lastHash[3] >= 'b' && lastHash[3] <= 'f'
+	}
+	return false
+}
+
+func currPos(path string) (int, int) {
+	var cX, cY int
+	for i := range path {
+		switch path[i] {
+		case 'U':
+			cY--
+		case 'D':
+			cY++
+		case 'L':
+			cX--
+		case 'R':
+			cX++
+		}
+	}
+	return cX, cY
+}
+
+func PrintState(path, passcode string) {
+}
+
+func printUsageAndExit() {
+	fmt.Println("Usage: ./day17 <passcode> <gridWidth> <gridHeight>")
+	os.Exit(0)
+}