广度优先搜索（breadth-first-search）

from collections import deque

def person_is_seller(name):
      return name[-1] == 'm'

graph = {}
graph["you"] = ["alice", "bob", "claire"]
graph["bob"] = ["anuj", "peggy"]
graph["alice"] = ["peggy"]
graph["claire"] = ["thom", "jonny"]
graph["anuj"] = []
graph["peggy"] = []
graph["thom"] = []
graph["jonny"] = []

def search(name):
    search_queue = deque()
    search_queue += graph[name]
    # This array is how you keep track of which people you've searched before.
    searched = []
    while search_queue:
        person = search_queue.popleft()
        # Only search this person if you haven't already searched them.
        if not person in searched:
            if person_is_seller(person):
                print(person + " is a mango seller!")
                return True
            else:
                search_queue += graph[person]
                # Marks this person as searched
                searched.append(person)
    return False

search("you")

小结

1. 广度优先搜索指出是否有从A到B的路径。如果有，广度优先搜索将找出最短路径。
2. 你需要按加入顺序检查搜索列表中的人，否则找到的就不是最短路径，因此搜索列表必须是队列。
3. 对于检查过的人，务必不要再去检查，否则可能导致无限循环