python实现A算法8数码

A*算法是一种启发式搜索算法，可以用于解决8数码问题。下面是python实现A*算法8数码的代码：

import heapq

class Board:
    def __init__(self, start_state, goal_state):
        self.start_state = start_state
        self.goal_state = goal_state
        self.blank_idx = start_state.index(0)
        self.goal_idx = None
        self.calc_goal_idx()
        self.g = 0
        self.h = self.heuristic()
        self.f = self.g + self.h

    def calc_goal_idx(self):
        for i in range(9):
            if self.goal_state[i] != self.start_state[i]:
                self.goal_idx = self.goal_state.index(self.start_state[i])
                break

    def heuristic(self):
        manhattan = 0
        for i in range(9):
            if self.start_state[i] != 0:
                manhattan += abs(i // 3 - self.goal_idx // 3) + abs(i % 3 - self.goal_idx % 3)
        return manhattan

    def move_blank(self, idx):
        new_state = self.start_state.copy()
        new_state[self.blank_idx], new_state[idx] = new_state[idx], new_state[self.blank_idx]
        return Board(new_state, self.goal_state)

    def __lt__(self, other):
        return self.f < other.f

def a_star(start_state, goal_state):
    open_list = []
    closed_list = set()

    start_board = Board(start_state, goal_state)
    heapq.heappush(open_list, start_board)

    while open_list:
        cur_board = heapq.heappop(open_list)
        if cur_board.start_state == goal_state:
            return cur_board.g

        closed_list.add(tuple(cur_board.start_state))

        for move_idx in [-3, 3, -1, 1]:
            if cur_board.blank_idx % 3 == 0 and move_idx == -1:
                continue
            if cur_board.blank_idx % 3 == 2 and move_idx == 1:
                continue
            new_blank_idx = cur_board.blank_idx + move_idx
            if new_blank_idx < 0 or new_blank_idx >= 9:
                continue
            if abs(move_idx) == 3:
                if move_idx < 0:
                    new_board = cur_board.move_blank(cur_board.blank_idx - 3)
                else:
                    new_board = cur_board.move_blank(cur_board.blank_idx + 3)
            else:
                new_board = cur_board.move_blank(new_blank_idx)

            if tuple(new_board.start_state) in closed_list:
                continue

            new_board.g = cur_board.g + 1
            new_board.h = new_board.heuristic()
            new_board.f = new_board.g + new_board.h

            heapq.heappush(open_list, new_board)

    return -1

if __name__ == '__main__':
    start_state = [1, 2, 3, 4, 5, 6, 0, 7, 8]
    goal_state = [0, 1, 2, 3, 4, 5, 6, 7, 8]
    moves = a_star(start_state, goal_state)
    print("Minimum number of moves required:", moves)

此代码实现了A*算法解决8数码问题。输入开始状态和目标状态，输出移动最少的步数。