2026-rff_mp/SorokinAD/[2]lab_2/strategies.py

from abc import ABC, abstractmethod
from collections import deque
from heapq import heappush, heappop

from maze import Maze
from cell import Cell


class PathFindingStrategy(ABC):

    @abstractmethod
    def find_path(
        self,
        maze: Maze,
        start: Cell,
        exit: Cell
    ) -> tuple[list[Cell], int]:

        pass


# =========================================================
# BFS
# =========================================================

class BFSStrategy(PathFindingStrategy):

    def find_path(self, maze, start, exit):

        queue = deque([start])

        visited = {start}
        parent = {}

        visited_count = 0

        while queue:

            current = queue.popleft()

            visited_count += 1

            if current == exit:
                path = self._restore_path(parent, start, exit)
                return path, visited_count

            for neighbor in maze.get_neighbors(current):

                if neighbor not in visited:

                    visited.add(neighbor)

                    parent[neighbor] = current

                    queue.append(neighbor)

        return [], visited_count

    @staticmethod
    def _restore_path(parent, start, exit):

        path = []

        current = exit

        while current != start:
            path.append(current)
            current = parent[current]

        path.append(start)

        path.reverse()

        return path


# =========================================================
# DFS
# =========================================================

class DFSStrategy(PathFindingStrategy):

    def find_path(self, maze, start, exit):

        stack = [start]

        visited = {start}
        parent = {}

        visited_count = 0

        while stack:

            current = stack.pop()

            visited_count += 1

            if current == exit:
                path = self._restore_path(parent, start, exit)
                return path, visited_count

            for neighbor in maze.get_neighbors(current):

                if neighbor not in visited:

                    visited.add(neighbor)

                    parent[neighbor] = current

                    stack.append(neighbor)

        return [], visited_count

    @staticmethod
    def _restore_path(parent, start, exit):

        path = []

        current = exit

        while current != start:
            path.append(current)
            current = parent[current]

        path.append(start)

        path.reverse()

        return path


# =========================================================
# A*
# =========================================================

class AStarStrategy(PathFindingStrategy):

    def heuristic(self, cell: Cell, exit: Cell):

        return abs(cell.x - exit.x) + abs(cell.y - exit.y)

    def find_path(self, maze, start, exit):

        open_set = []

        heappush(open_set, (0, start.x, start.y, start))

        g_score = {
            start: 0
        }

        parent = {}

        visited = set()

        visited_count = 0

        while open_set:

            _, _, _, current = heappop(open_set)

            if current in visited:
                continue

            visited.add(current)

            visited_count += 1

            if current == exit:
                path = self._restore_path(parent, start, exit)
                return path, visited_count

            for neighbor in maze.get_neighbors(current):

                tentative_g = g_score[current] + 1

                if (
                    neighbor not in g_score
                    or tentative_g < g_score[neighbor]
                ):

                    g_score[neighbor] = tentative_g

                    f_score = tentative_g + self.heuristic(
                        neighbor,
                        exit
                    )

                    parent[neighbor] = current

                    heappush(
                        open_set,
                        (
                            f_score,
                            neighbor.x,
                            neighbor.y,
                            neighbor
                        )
                    )

        return [], visited_count

    @staticmethod
    def _restore_path(parent, start, exit):

        path = []

        current = exit

        while current != start:
            path.append(current)
            current = parent[current]

        path.append(start)

        path.reverse()

        return path