1.Python有序字典
dict = collections.OrderedDict()
dict.move_to_end(key)
dict.popitem(last=False) # last = False,先进先出.
2.
from collections import defaultdict
graph = defaultdict(list)
for x,y in edges:
graph[x].append(y)
graph[y].append(x)
heapq.nlargest: