solve 6 pt 2

6/main.go

@@ -18,26 +18,52 @@ func main() {
 	_ = f.Close()
 
 	start := time.Now()
-	res := countGuardSpaces(guardMap, guard)
+	res, _ := countGuardSpaces(guardMap, guard)
 	elapsed := time.Since(start)
 	fmt.Println(res)
 	fmt.Println(elapsed)
 
-	//start2 := time.Now()
-	//res2 := countMiddleOfCorrectedOrders(rules, orders)
-	//elapsed2 := time.Since(start2)
-	//fmt.Println(res2)
-	//fmt.Println(elapsed2)
+	start2 := time.Now()
+	res2 := countPossibleLoops(guardMap, guard)
+	elapsed2 := time.Since(start2)
+	fmt.Println(res2)
+	fmt.Println(elapsed2)
 }
 
-func countGuardSpaces(guardMap [][]bool, guard guardPosition) int {
+// this is brute force nonsense. I have might be able to do better by restricting to locations where we have visited
+// at least once. That would cut down the search space significantly. I think there might even be a far more
+// effecient solution out there that would require using a graph of paths instead and finding a loop? unsure.
+// a 2s run time is pathetic though.
+func countPossibleLoops(guardMap [][]bool, guard guardPosition) int {
+	var acc int
+	for j := 0; j < len(guardMap); j++ {
+		for i := 0; i < len(guardMap[j]); i++ {
+			if !guardMap[j][i] && !(j == guard.y && i == guard.x) {
+				guardMap[j][i] = true
+				_, loop := countGuardSpaces(guardMap, guard)
+				if loop {
+					acc++
+				}
+				guardMap[j][i] = false
+			}
+		}
+	}
+	return acc
+}
+
+func countGuardSpaces(guardMap [][]bool, guard guardPosition) (int, bool) {
 	// assume the guard is on the map someplace
 	acc := 1
-	visited := make([][]bool, 0, len(guardMap))
+	visited := make([][][]bool, 0, len(guardMap))
 	for _, _ = range guardMap {
-		visited = append(visited, make([]bool, len(guardMap[0])))
+		visitLine := make([][]bool, len(guardMap[0]))
+		for i, _ := range visitLine {
+			// 4 directions plus 1 ignored
+			visitLine[i] = make([]bool, 5)
+		}
+		visited = append(visited, visitLine)
 	}
-	visited[guard.y][guard.x] = true
+	visited[guard.y][guard.x][guard.d] = true
 
 	for guard.x >= 0 && guard.x < len(guardMap[0]) && guard.y >= 0 && guard.y < len(guardMap) {
 		var nextX int
@@ -70,16 +96,27 @@ func countGuardSpaces(guardMap [][]bool, guard guardPosition) int {
 				guard.d = Dir_DOWN
 			}
 		} else {
-			if ok && !visited[nextY][nextX] {
-				visited[nextY][nextX] = true
-				acc++
+			if ok {
+				if visited[nextY][nextX][guard.d] { // loop detected, we have already been to the next space in the same direction
+					return acc, true
+				}
+
+				// no loop but have we ever been here?
+				var seen bool
+				for i := 0; !seen && i < len(visited[nextY][nextX]); i++ {
+					seen = visited[nextY][nextX][i]
+				}
+				if !seen {
+					visited[nextY][nextX][guard.d] = true
+					acc++
+				}
 			}
 			guard.x = nextX
 			guard.y = nextY
 		}
 	}
 
-	return acc
+	return acc, false
 }
 
 type direction int

6/main_test.go

@@ -97,8 +97,47 @@ func Test_countGuardSpaces(t *testing.T) {
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			if got := countGuardSpaces(tt.args.guardMap, tt.args.guard); got != tt.want {
-				t.Errorf("countGuardSpaces() = %v, want %v", got, tt.want)
+			if got, loop := countGuardSpaces(tt.args.guardMap, tt.args.guard); got != tt.want || loop {
+				t.Errorf("countGuardSpaces() = %v, %v, want %v, false", got, loop, tt.want)
+			}
+		})
+	}
+}
+
+func Test_countPossibleLoops(t *testing.T) {
+	type args struct {
+		guardMap [][]bool
+		guard    guardPosition
+	}
+	tests := []struct {
+		name string
+		args args
+		want int
+	}{
+		{
+			name: "example",
+			args: args{
+				guard: guardPosition{x: 4, y: 6, d: Dir_UP},
+				guardMap: [][]bool{
+					{false, false, false, false, true, false, false, false, false, false},
+					{false, false, false, false, false, false, false, false, false, true},
+					{false, false, false, false, false, false, false, false, false, false},
+					{false, false, true, false, false, false, false, false, false, false},
+					{false, false, false, false, false, false, false, true, false, false},
+					{false, false, false, false, false, false, false, false, false, false},
+					{false, true, false, false, false /* guard pos */, false, false, false, false, false},
+					{false, false, false, false, false, false, false, false, true, false},
+					{true, false, false, false, false, false, false, false, false, false},
+					{false, false, false, false, false, false, true, false, false, false},
+				},
+			},
+			want: 6,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := countPossibleLoops(tt.args.guardMap, tt.args.guard); got != tt.want {
+				t.Errorf("countPossibleLoops() = %v, want %v", got, tt.want)
 			}
 		})
 	}