Fix greedy_best_first (TheAlgorithms#8775)

* fix: typo TheAlgorithms#8770 * refactor: delete unnecessary continue * add test grids * fix: add \_\_eq\_\_ in Node class TheAlgorithms#8770 * fix: delete unnecessary code - node in self.open_nodes is always better node TheAlgorithms#8770 * fix: docstring * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * fix: docstring max length * refactor: get the successors using a list comprehension * Apply suggestions from code review --------- Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com> Co-authored-by: Tianyi Zheng <tianyizheng02@gmail.com>

Author: 3 people

graphs/greedy_best_first.py

@@ -6,14 +6,32 @@
 
 Path = list[tuple[int, int]]
 
-grid = [
- [0, 0, 0, 0, 0, 0, 0],
- [0, 1, 0, 0, 0, 0, 0], # 0 are free path whereas 1's are obstacles
- [0, 0, 0, 0, 0, 0, 0],
- [0, 0, 1, 0, 0, 0, 0],
- [1, 0, 1, 0, 0, 0, 0],
- [0, 0, 0, 0, 0, 0, 0],
- [0, 0, 0, 0, 1, 0, 0],
+# 0's are free path whereas 1's are obstacles
+TEST_GRIDS = [
+ [
+ [0, 0, 0, 0, 0, 0, 0],
+ [0, 1, 0, 0, 0, 0, 0],
+ [0, 0, 0, 0, 0, 0, 0],
+ [0, 0, 1, 0, 0, 0, 0],
+ [1, 0, 1, 0, 0, 0, 0],
+ [0, 0, 0, 0, 0, 0, 0],
+ [0, 0, 0, 0, 1, 0, 0],
+ ],
+ [
+ [0, 0, 0, 1, 1, 0, 0],
+ [0, 0, 0, 0, 1, 0, 1],
+ [0, 0, 0, 1, 1, 0, 0],
+ [0, 1, 0, 0, 1, 0, 0],
+ [1, 0, 0, 1, 1, 0, 1],
+ [0, 0, 0, 0, 0, 0, 0],
+ ],
+ [
+ [0, 0, 1, 0, 0],
+ [0, 1, 0, 0, 0],
+ [0, 0, 1, 0, 1],
+ [1, 0, 0, 1, 1],
+ [0, 0, 0, 0, 0],
+ ],
 ]
 
 delta = ([-1, 0], [0, -1], [1, 0], [0, 1]) # up, left, down, right
@@ -65,10 +83,14 @@ def calculate_heuristic(self) -> float:
  def __lt__(self, other) -> bool:
  return self.f_cost < other.f_cost
 
+ def __eq__(self, other) -> bool:
+ return self.pos == other.pos
+
 
 class GreedyBestFirst:
  """
- >>> gbf = GreedyBestFirst((0, 0), (len(grid) - 1, len(grid[0]) - 1))
+ >>> grid = TEST_GRIDS[2]
+ >>> gbf = GreedyBestFirst(grid, (0, 0), (len(grid) - 1, len(grid[0]) - 1))
  >>> [x.pos for x in gbf.get_successors(gbf.start)]
  [(1, 0), (0, 1)]
  >>> (gbf.start.pos_y + delta[3][0], gbf.start.pos_x + delta[3][1])
@@ -78,11 +100,14 @@ class GreedyBestFirst:
  >>> gbf.retrace_path(gbf.start)
  [(0, 0)]
  >>> gbf.search() # doctest: +NORMALIZE_WHITESPACE
- [(0, 0), (1, 0), (2, 0), (3, 0), (3, 1), (4, 1), (5, 1), (6, 1),
- (6, 2), (6, 3), (5, 3), (5, 4), (5, 5), (6, 5), (6, 6)]
+ [(0, 0), (1, 0), (2, 0), (2, 1), (3, 1), (4, 1), (4, 2), (4, 3),
+ (4, 4)]
  """
 
- def __init__(self, start: tuple[int, int], goal: tuple[int, int]):
+ def __init__(
+ self, grid: list[list[int]], start: tuple[int, int], goal: tuple[int, int]
+ ):
+ self.grid = grid
  self.start = Node(start[1], start[0], goal[1], goal[0], 0, None)
  self.target = Node(goal[1], goal[0], goal[1], goal[0], 99999, None)
 
@@ -114,14 +139,6 @@ def search(self) -> Path | None:
 
  if child_node not in self.open_nodes:
  self.open_nodes.append(child_node)
- else:
- # retrieve the best current path
- better_node = self.open_nodes.pop(self.open_nodes.index(child_node))
-
- if child_node.g_cost < better_node.g_cost:
- self.open_nodes.append(child_node)
- else:
- self.open_nodes.append(better_node)
 
  if not self.reached:
  return [self.start.pos]
@@ -131,28 +148,22 @@ def get_successors(self, parent: Node) -> list[Node]:
  """
  Returns a list of successors (both in the grid and free spaces)
  """
- successors = []
- for action in delta:
- pos_x = parent.pos_x + action[1]
- pos_y = parent.pos_y + action[0]
-
- if not (0 <= pos_x <= len(grid[0]) - 1 and 0 <= pos_y <= len(grid) - 1):
- continue
-
- if grid[pos_y][pos_x] != 0:
- continue
-
- successors.append(
- Node(
- pos_x,
- pos_y,
- self.target.pos_y,
- self.target.pos_x,
- parent.g_cost + 1,
- parent,
- )
+ return [
+ Node(
+ pos_x,
+ pos_y,
+ self.target.pos_x,
+ self.target.pos_y,
+ parent.g_cost + 1,
+ parent,
+ )
+ for action in delta
+ if (
+ 0 <= (pos_x := parent.pos_x + action[1]) < len(self.grid[0])
+ and 0 <= (pos_y := parent.pos_y + action[0]) < len(self.grid)
+ and self.grid[pos_y][pos_x] == 0
  )
- return successors
+ ]
 
  def retrace_path(self, node: Node | None) -> Path:
  """
@@ -168,18 +179,21 @@ def retrace_path(self, node: Node | None) -> Path:
 
 
 if __name__ == "__main__":
- init = (0, 0)
- goal = (len(grid) - 1, len(grid[0]) - 1)
- for elem in grid:
- print(elem)
-
- print("------")
-
- greedy_bf = GreedyBestFirst(init, goal)
- path = greedy_bf.search()
- if path:
- for pos_x, pos_y in path:
- grid[pos_x][pos_y] = 2
+ for idx, grid in enumerate(TEST_GRIDS):
+ print(f"==grid-{idx + 1}==")
 
+ init = (0, 0)
+ goal = (len(grid) - 1, len(grid[0]) - 1)
  for elem in grid:
  print(elem)
+
+ print("------")
+
+ greedy_bf = GreedyBestFirst(grid, init, goal)
+ path = greedy_bf.search()
+ if path:
+ for pos_x, pos_y in path:
+ grid[pos_x][pos_y] = 2
+
+ for elem in grid:
+ print(elem)