这是一类典型的bfs问题,希望下次遇到我能回
import collections
class Solution(object):
    def openLock1(self, deadends, target):
        dead_set = set(deadends)
        queue = collections.deque()
        queue.append(("0000", 0))
        visited = {"0000"}

        while queue:
            number, depth = queue.popleft()
            if number == target:
                return depth

            if number in dead_set:
                continue

            for item in self.neighbors(number):
                # 如果该节点访问过了,再次访问会导致死循环
                if item not in visited:
                    visited.add(item)
                    queue.append((item, depth + 1))
        return -1

    def neighbors(self, number):
        for i in range(len(number)):
            cur = int(number[i])
            for drift in (-1, 1):
                temp = (cur + drift) % 10
                yield number[:i] + str(temp) + number[i+1:]

    def openLock(self, deadends, target):
        dead_set = set(deadends)
        start_set = {"0000"}
        target_set = {target}

        visited_set = set()
        depth = 0
        while start_set and target_set:
            temp = set()
            for cur in start_set:
                if cur in dead_set:
                    continue
                if cur in target_set:
                    return depth
                visited_set.add(cur)
                for item in self.neighbors(cur):
                    if item not in visited_set:
                        temp.add(item)

            depth += 1
            start_set = target_set
            target_set = temp
        return -1


if __name__ == '__main__':
    deadends = ["0201", "0101", "0102", "1212", "2002"]
    target = "0202"
    s1 = Solution()
    root = s1.openLock(deadends, target)
    print(root)