Pretify binary maze.

src/hacker-rank/BinaryMaze.cs

@@ -22,30 +22,27 @@ namespace CodingInterview.HackerRank
 		/// <returns>a series of movements describing the shortest path from Y to X</returns>
 		public List<char> Solve((int i, int j) start, char[,] map)
 		{
+			// BFS queue
 			var queue = new Queue<((int i, int j) tile, List<char> path)>();
+			// start with a starting tile
 			queue.Enqueue((tile: start, path: new List<char>()));
 
+			// done when all reachable tiles are visited, or earlier
 			while (queue.Count > 0)
 			{
+				// get next tile
 				var (location, path) = queue.Dequeue();
 
-				if (
-					location.i < 0 || location.i == map.GetLength(0) ||
-					location.j < 0 || location.j == map.GetLength(1) ||
-					map[location.i, location.j] == '0' ||
-					map[location.i, location.j] == '2'
-				)
-				{
-					continue;
-				}
-
+				// if it the target tile, we are done
 				if (map[location.i, location.j] == 'X')
 				{
 					return path;
 				}
 
+				// mark visited
 				map[location.i, location.j] = '2';
 
+				// try all possible directions (4 in this case)
 				foreach (var direction in new (int i, int j, char where)[] {
 					(0, +1, 'r'),
 					(0, -1, 'l'),
@@ -53,15 +50,35 @@ namespace CodingInterview.HackerRank
 					(-1, 0, 'u')
 				})
 				{
+					// compute next tile
+					var newLocation = (i: location.i + direction.i, j: location.j + direction.j);
+
+					// do not add to queue if our of maze
+					if (newLocation.i < 0 || newLocation.i == map.GetLength(0) ||
+						newLocation.j < 0 || newLocation.j == map.GetLength(1)
+					)
+					{
+						continue;
+					}
+
+					// do not add to queue if blockade or visited
+					if (map[newLocation.i, newLocation.j] == '0' ||
+						map[newLocation.i, newLocation.j] == '2')
+					{
+						continue;
+					}
+
+					// otherwise add the next tile and update its path
 					var @copy = new List<char>(path);
 					@copy.Add(direction.where);
 					queue.Enqueue((
-						tile: (i: location.i + direction.i, j: location.j + direction.j),
+						tile: newLocation,
 						path: @copy
 					));
 				}
 			}
 
+			// if target cannot be reached, return empty path
 			return new List<char>();
 		}