2026-rff_mp/zhigalovrd/lab2/strategies.py

from abc import ABC, abstractmethod
from collections import deque
from typing import List, Tuple, Dict, Optional
import heapq
from maze import Maze, Cell

class PathFindingStrategy(ABC):
    @abstractmethod
    def find_path(self, maze: Maze, start: Optional[Cell], exit: Optional[Cell]) -> Tuple[List[Cell], int]:
        pass

class BFSStrategy(PathFindingStrategy):
    def find_path(self, maze: Maze, start: Optional[Cell], exit: Optional[Cell]) -> Tuple[List[Cell], int]:
        if start is None or exit is None:
            return [], 0
        queue = deque([start])
        visited = {start}
        parent = {start: None}
        while queue:
            current = queue.popleft()
            if current is exit:
                return self._reconstruct_path(parent, exit), len(visited)
            for nb in maze.get_neighbors(current):
                if nb not in visited:
                    visited.add(nb)
                    parent[nb] = current
                    queue.append(nb)
        return [], len(visited)

    def _reconstruct_path(self, parent: Dict[Cell, Optional[Cell]], end: Cell) -> List[Cell]:
        path = []
        cur = end
        while cur is not None:
            path.append(cur)
            cur = parent[cur]
        path.reverse()
        return path

class DFSStrategy(PathFindingStrategy):
    def find_path(self, maze: Maze, start: Optional[Cell], exit: Optional[Cell]) -> Tuple[List[Cell], int]:
        if start is None or exit is None:
            return [], 0
        stack = [(start, [start])]
        visited = {start}
        while stack:
            current, path = stack.pop()
            if current is exit:
                return path, len(visited)
            for nb in maze.get_neighbors(current):
                if nb not in visited:
                    visited.add(nb)
                    stack.append((nb, path + [nb]))
        return [], len(visited)

class AStarStrategy(PathFindingStrategy):
    @staticmethod
    def heuristic(a: Cell, b: Cell) -> int:
        return abs(a.x - b.x) + abs(a.y - b.y)

    def find_path(self, maze: Maze, start: Optional[Cell], exit: Optional[Cell]) -> Tuple[List[Cell], int]:
        if start is None or exit is None:
            return [], 0
        open_set = []
        heapq.heappush(open_set, (0, start))
        came_from = {}
        g_score = {start: 0}
        f_score = {start: self.heuristic(start, exit)}
        visited_count = 0

        while open_set:
            _, current = heapq.heappop(open_set)
            visited_count += 1
            if current is exit:
                path = self._reconstruct_path(came_from, exit)
                return path, visited_count
            for nb in maze.get_neighbors(current):
                tentative_g = g_score[current] + 1
                if nb not in g_score or tentative_g < g_score[nb]:
                    came_from[nb] = current
                    g_score[nb] = tentative_g
                    f_score[nb] = tentative_g + self.heuristic(nb, exit)
                    heapq.heappush(open_set, (f_score[nb], nb))
        return [], visited_count

    def _reconstruct_path(self, came_from: Dict[Cell, Cell], current: Cell) -> List[Cell]:
        path = [current]
        while current in came_from:
            current = came_from[current]
            path.append(current)
        path.reverse()
        return path