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Task/Maze-solving/Ruby/maze-solving.rb

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+class Maze
+  # Solve via breadth-first algorithm.
+  # Each queue entry is a path, that is list of coordinates with the
+  # last coordinate being the one that shall be visited next.
+  def solve
+
+    # Clean up.
+    reset_visiting_state
+
+    # Enqueue start position.
+    @queue = []
+    enqueue_cell([], @start_x, @start_y)
+
+    # Loop as long as there are cells to visit and no solution has
+    # been found yet.
+    path = nil
+    until path || @queue.empty?
+      path = solve_visit_cell
+    end
+
+    if path
+      # Mark the cells that make up the shortest path.
+      for x, y in path
+        @path[x][y] = true
+      end
+    else
+      puts "No solution found?!"
+    end
+  end
+
+  private
+
+  # Maze solving visiting method.
+  def solve_visit_cell
+    # Get the next path.
+    path = @queue.shift
+    # The cell to visit is the last entry in the path.
+    x, y = path.last
+
+    # Have we reached the end yet?
+    return path  if x == @end_x && y == @end_y
+
+    # Mark cell as visited.
+    @visited[x][y] = true
+
+    for dx, dy in DIRECTIONS
+      if dx.nonzero?
+        # Left / Right
+        new_x = x + dx
+        if move_valid?(new_x, y) && !@vertical_walls[ [x, new_x].min ][y]
+          enqueue_cell(path, new_x, y)
+        end
+      else
+        # Top / Bottom
+        new_y = y + dy
+        if move_valid?(x, new_y) && !@horizontal_walls[x][ [y, new_y].min ]
+          enqueue_cell(path, x, new_y)
+        end
+      end
+    end
+
+    nil         # No solution yet.
+  end
+
+  # Enqueue a new coordinate to visit.
+  def enqueue_cell(path, x, y)
+    # Add new coordinates to the current path and enqueue the new path.
+    @queue << path + [[x, y]]
+  end
+end
+
+# Demonstration:
+maze = Maze.new 20, 10
+maze.solve
+maze.print