Fix mypy errors at greedy best first algo (#4575)

graphs/greedy_best_first.py

@@ -4,6 +4,10 @@ https://en.wikipedia.org/wiki/Best-first_search#Greedy_BFS
 
 from __future__ import annotations
 
+from typing import Optional
+
+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
@@ -33,7 +37,15 @@ class Node:
     True
     """
 
-    def __init__(self, pos_x, pos_y, goal_x, goal_y, g_cost, parent):
+    def __init__(
+        self,
+        pos_x: int,
+        pos_y: int,
+        goal_x: int,
+        goal_y: int,
+        g_cost: float,
+        parent: Optional[Node],
+    ):
         self.pos_x = pos_x
         self.pos_y = pos_y
         self.pos = (pos_y, pos_x)
@@ -72,16 +84,16 @@ class GreedyBestFirst:
      (6, 2), (6, 3), (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], 0, None)
         self.target = Node(goal[1], goal[0], goal[1], goal[0], 99999, None)
 
         self.open_nodes = [self.start]
-        self.closed_nodes = []
+        self.closed_nodes: list[Node] = []
 
         self.reached = False
 
-    def search(self) -> list[tuple[int]]:
+    def search(self) -> Optional[Path]:
         """
         Search for the path,
         if a path is not found, only the starting position is returned
@@ -113,8 +125,9 @@ class GreedyBestFirst:
                     else:
                         self.open_nodes.append(better_node)
 
-        if not (self.reached):
+        if not self.reached:
             return [self.start.pos]
+        return None
 
     def get_successors(self, parent: Node) -> list[Node]:
         """
@@ -143,7 +156,7 @@ class GreedyBestFirst:
             )
         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
         """
@@ -166,9 +179,9 @@ if __name__ == "__main__":
 
     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 elem in path:
-        grid[elem[0]][elem[1]] = 2
-
-    for elem in grid:
-        print(elem)
+        for elem in grid:
+            print(elem)