Fix mypy errors at bidirectional_bfs (#4531)

Author: mhihasan

graphs/bidirectional_breadth_first_search.py

@@ -5,6 +5,9 @@
 from __future__ import annotations
 
 import time
+from typing import Optional
+
+Path = list[tuple[int, int]]
 
 grid = [
     [0, 0, 0, 0, 0, 0, 0],
@@ -20,7 +23,9 @@
 
 
 class Node:
-    def __init__(self, pos_x, pos_y, goal_x, goal_y, parent):
+    def __init__(
+        self, pos_x: int, pos_y: int, goal_x: int, goal_y: int, parent: Optional[Node]
+    ):
         self.pos_x = pos_x
         self.pos_y = pos_y
         self.pos = (pos_y, pos_x)
@@ -45,14 +50,14 @@ class BreadthFirstSearch:
      (5, 1), (5, 2), (5, 3), (5, 4), (5, 5), (6, 5), (6, 6)]
     """
 
-    def __init__(self, start, goal):
+    def __init__(self, start: tuple[int, int], goal: tuple[int, int]):
         self.start = Node(start[1], start[0], goal[1], goal[0], None)
         self.target = Node(goal[1], goal[0], goal[1], goal[0], None)
 
         self.node_queue = [self.start]
         self.reached = False
 
-    def search(self) -> list[tuple[int]]:
+    def search(self) -> Optional[Path]:
         while self.node_queue:
             current_node = self.node_queue.pop(0)
 
@@ -65,8 +70,9 @@ def search(self) -> list[tuple[int]]:
             for node in successors:
                 self.node_queue.append(node)
 
-        if not (self.reached):
-            return [(self.start.pos)]
+        if not self.reached:
+            return [self.start.pos]
+        return None
 
     def get_successors(self, parent: Node) -> list[Node]:
         """
@@ -87,7 +93,7 @@ def get_successors(self, parent: Node) -> list[Node]:
             )
         return successors
 
-    def retrace_path(self, node: Node) -> list[tuple[int]]:
+    def retrace_path(self, node: Optional[Node]) -> Path:
         """
         Retrace the path from parents to parents until start node
         """
@@ -119,7 +125,7 @@ def __init__(self, start, goal):
         self.bwd_bfs = BreadthFirstSearch(goal, start)
         self.reached = False
 
-    def search(self) -> list[tuple[int]]:
+    def search(self) -> Optional[Path]:
         while self.fwd_bfs.node_queue or self.bwd_bfs.node_queue:
             current_fwd_node = self.fwd_bfs.node_queue.pop(0)
             current_bwd_node = self.bwd_bfs.node_queue.pop(0)
@@ -144,10 +150,9 @@ def search(self) -> list[tuple[int]]:
 
         if not self.reached:
             return [self.fwd_bfs.start.pos]
+        return None
 
-    def retrace_bidirectional_path(
-        self, fwd_node: Node, bwd_node: Node
-    ) -> list[tuple[int]]:
+    def retrace_bidirectional_path(self, fwd_node: Node, bwd_node: Node) -> Path:
         fwd_path = self.fwd_bfs.retrace_path(fwd_node)
         bwd_path = self.bwd_bfs.retrace_path(bwd_node)
         bwd_path.pop()