Add Aldous-Broder algorithm. Make image demo open generated image under Linux

Author: Kartones

README.md

@@ -8,6 +8,7 @@ A small remark: Code is not a 1:1 copy of the book's. For example I built render
 
 ## Implemented algorithms
 
+- `AldousBroder`
 - `BinaryTree`
 - `Sidewinder`
 

algorithms/aldous_broder.py

@@ -0,0 +1,28 @@
+from random import choice
+
+from base.grid import Grid
+
+"""
+Aldous-Broder algorithm works by always choosing a random neighbor of the current cell and linking them if not yet
+visited ("random walking"), repeating until all cells are visited once.
+Can take long to compute on big grids.
+"""
+
+
+class AldousBroder:
+
+    @staticmethod
+    def on(grid: Grid) -> Grid:
+        current_cell = grid.random_cell()
+        unvisited_count = grid.size - 1
+
+        while unvisited_count > 0:
+            neighbor = choice(current_cell.neighbors())
+            if neighbor is None:
+                raise ValueError("Aldous-Broder algorithm needs all cells to have at least one neighbor")
+            if len(neighbor.links) == 0:
+                current_cell.link(neighbor)
+                unvisited_count -= 1
+            current_cell = neighbor
+
+        return grid

base/grid.py

@@ -14,6 +14,10 @@ def rows(self) -> int:
     def columns(self) -> int:
         return self._columns
 
+    @property
+    def size(self) -> int:
+        return self.rows * self.columns
+
     def __init__(self, rows: int, columns: int) -> None:
         if rows is None or rows < 0:
             raise ValueError("Rows must be a positive integer")
@@ -47,9 +51,6 @@ def random_cell(self) -> Cell:
         row = randint(0, self.rows - 1)
         return cast(Cell, self.get_cell(row, column))
 
-    def size(self) -> int:
-        return self.rows * self.columns
-
     def each_row(self) -> Generator:
         for row in range(self.rows):
             yield self._grid[row]

demos/demo_utils.py

@@ -3,11 +3,13 @@
 
 from algorithms.binary_tree import BinaryTree
 from algorithms.sidewinder import Sidewinder
+from algorithms.aldous_broder import AldousBroder
+
 import renderers.ascii_renderer as ASCIIRenderer
 import renderers.unicode_renderer as UNICODERenderer
 import renderers.png_renderer as PNGRenderer
 
-ALGORITHMS = [BinaryTree, Sidewinder]
+ALGORITHMS = [BinaryTree, Sidewinder, AldousBroder]
 ALL_RENDERERS = [UNICODERenderer, ASCIIRenderer, PNGRenderer]
 
 

demos/image_demo.py

@@ -1,3 +1,7 @@
+import platform
+import subprocess
+from time import gmtime, strftime
+
 import args
 from typing import cast, Union     # noqa: F401
 
@@ -68,4 +72,9 @@ def get_coloring() -> bool:
             raise IndexError("Invalid start cell row {} column {}".format(start_row, start_column))
         grid.distances = start_cell.distances()     # type: ignore
 
-    renderer.render(grid, coloring=coloring)
+    filename = strftime("%Y%m%d%H%M%S", gmtime())
+
+    renderer.render(grid, coloring=coloring, filename=filename)
+
+    if platform.system() == "Linux":
+        subprocess.run(["xdg-open", "{}.png".format(filename)])

test/test_grid.py

@@ -59,6 +59,6 @@ def test_random_cell() -> None:
 
 
 def test_size() -> None:
-    assert Grid(1, 1).size() == 1
-    assert Grid(2, 2).size() == 4
-    assert Grid(3, 3).size() == 9
+    assert Grid(1, 1).size == 1
+    assert Grid(2, 2).size == 4
+    assert Grid(3, 3).size == 9