LeetCode-【图论BFS】打开转盘锁

        if target == "0000":
            return 0
            
        def get(status:str)->Generator[str, None, None]:
            s = list(status)
            for i in range(4):
                num = s[i]
                s[i] = num_prev(num)
                yield "".join(s)
                s[i] = num_next(num)
                yield "".join(s)
                s[i] = num         



        q = [AStar("0000", target, 0)]
        seen = {"0000"}
        while q:
            node = heappop(q)
            for next_status in get(node.status):
                if next_status not in seen and next_status not in  dead:
                    if target==next_status:
                        return node.g + 1
                    heapq.heappush(q, AStar(next_status, target, node.g + 1))
                    seen.add(next_status)
        return -1

说明：

队列可以使用deque 或者优先队列 heapq 模块需要一个seen 字典（查找时间复杂度较小）记录走过的状态把状态和步数(status , step)打包成整体放入队列get函数是一个生成器,Generator[str, None, None] 三个参数分别表示 yieldtype, sendtype, returntype 题目分析

本题可以采用BFS模板

也可采用A*算法，采用启发式距离
参考：AStar算法应用

class AStar:
    @staticmethod 
    def getH(status:str, target:str):
        ret = 0
        for i in range(4):
            dist = abs(int(status[i]) - int(target[i]))
            ret += min(dist, 10-dist)
        return ret 
    
    def __init__(self, status:str, target:str, g:str)->None:
        self.g = g 
        self.status = status
        self.h = AStar.getH(status,target)
        self.f = self.g + self.h 
    def __lt__(self, other:"AStar")->bool:
        return self.f  int:
        if target == "0000":
            return 0
        dead = set(deadends)
        if "0000" in dead:
            return -1

        def num_prev(x:str)->str:
            return '9' if x=='0' else str(int(x)-1)

        def num_next(x:str)->str:
            return '0' if x=='9' else str(int(x)+1)



        def get(status:str)->Generator[str, None, None]:
            s = list(status)
            for i in range(4):
                num = s[i]
                s[i] = num_prev(num)
                yield "".join(s)
                s[i] = num_next(num)
                yield "".join(s)
                s[i] = num         



        q = [AStar("0000", target, 0)]
        seen = {"0000"}
        while q:
            node = heappop(q)
            for next_status in get(node.status):
                if next_status not in seen and next_status not in  dead:
                    if target==next_status:
                        return node.g + 1
                    heapq.heappush(q, AStar(next_status, target, node.g + 1))
                    seen.add(next_status)
        return -1