Add Hunt-and-Kill algorithm

Author: Kartones

README.md

@@ -10,6 +10,7 @@ A small remark: Code is not a 1:1 copy of the book's. For example I built render
 
 - `AldousBroder`
 - `BinaryTree`
+- `HuntAndKill`
 - `Sidewinder`
 - `Wilson`
 

algorithms/hunt_and_kill.py

@@ -0,0 +1,41 @@
+from random import choice
+
+from typing import cast, Optional     # noqa: F401
+
+from base.grid import Grid
+from base.cell import Cell      # noqa: F401
+
+"""
+Hunt-and-Kill algorithm picks a random starting cell and randomly walks. It cannot walk on an already visited cell, and
+if finds at a dead-end (no more unvisited cells around current one), "hunts" from the northwest corner the first cell
+that is unvisted and has at least one visited neighbor; then starts walking again.
+"""
+
+
+class HuntAndKill:
+
+    @staticmethod
+    def on(grid: Grid) -> Grid:
+        current_cell = grid.random_cell()  # type: Optional[Cell]
+
+        while current_cell is not None:
+            unvisited_neighbors = \
+                [neighbor for neighbor in current_cell.neighbors if len(neighbor.links) == 0]  # type: ignore
+
+            if len(unvisited_neighbors) > 0:
+                # as long as there are unvisited paths, walk them
+                neighbor = cast(Cell, choice(unvisited_neighbors))
+                current_cell.link(neighbor)
+                current_cell = neighbor
+            else:
+                # enter hunt mode, find first unvisited cell near any visited cell
+                current_cell = None
+                for cell in grid.each_cell():
+                    visited_neighbors = [neighbor for neighbor in cell.neighbors if len(neighbor.links) > 0]
+                    if len(cell.links) == 0 and len(visited_neighbors) > 0:
+                        current_cell = cast(Cell, cell)
+                        neighbor = choice(visited_neighbors)
+                        current_cell.link(neighbor)
+                        break
+
+        return grid

demos/demo_utils.py

@@ -5,12 +5,13 @@
 from algorithms.sidewinder import Sidewinder
 from algorithms.aldous_broder import AldousBroder
 from algorithms.wilson import Wilson
+from algorithms.hunt_and_kill import HuntAndKill
 
 import renderers.ascii_renderer as ASCIIRenderer
 import renderers.unicode_renderer as UNICODERenderer
 import renderers.png_renderer as PNGRenderer
 
-ALGORITHMS = [BinaryTree, Sidewinder, AldousBroder, Wilson]
+ALGORITHMS = [AldousBroder, BinaryTree, HuntAndKill, Sidewinder, Wilson]
 ALL_RENDERERS = [UNICODERenderer, ASCIIRenderer, PNGRenderer]