[2] add Astar method

BudakovIS/docs/data/2-nd-exercize/main.py

@@ -1,5 +1,7 @@
 import sys
 from collections import deque
+import heapq
+from typing import List, Dict, Optional
 
 
 class Cell:
@@ -199,6 +201,45 @@ class DFSStrategy:
         return path
         
 
+class AStarStrategy:
+    def _heuristic(self, cell,exit_cell):
+        return abs(cell.x -exit_cell.x)+abs(cell.y-exit_cell.y)
+    def find_path(self,maze, start, exit_cell):
+        heap = []
+        counter = 0
+        start_f = 0 + self._heuristic(start,exit_cell)
+        heapq.heappush(heap, (start_f, counter, start))
+        counter +=1
+
+        came_from = {}
+        g_score = {start: 0}
+        f_score = {start: start_f}
+
+        while heap:
+            current_f, _, current = heapq.heappop(heap)
+            if current==exit_cell:
+                return self._reconstruct_path(came_from, start, exit_cell)
+            if current_f>f_score.get(current, float("inf")):
+                continue
+            for neighbor in maze.get_neighbors(current):
+                tentative_g = g_score[current] + 1
+                if tentative_g < g_score.get(neighbor, float('inf')):
+                    came_from[neighbor] = current
+                    g_score[neighbor] = tentative_g
+                    new_f = tentative_g + self._heuristic(neighbor, exit_cell)
+                    f_score[neighbor] = new_f
+                    heapq.heappush(heap, (new_f, counter, neighbor))
+                    counter += 1
+        return []
+    def _reconstruct_path(self, came_from, start, exit_cell):
+        path = []
+        current = exit_cell
+        while current is not None:
+            path.append(current)
+            current = came_from.get(current)
+        path.reverse()
+        return path
+
 if __name__ == "__main__":
     builder = TextFileMazeBuilder()
     maze = builder.build_from_file("maze1.txt")
@@ -211,3 +252,6 @@ if __name__ == "__main__":
     dfs = DFSStrategy()
     path = dfs.find_path(maze, maze.start, maze.exit)
     print(f"DFS: путь найден, длинна = {len(path)}")
+    astar = AStarStrategy()
+    path = astar.find_path(maze, maze.start, maze.exit)
+    print(f"A*: путь найден, длина = {len(path)}")