题目：
题解：
python
class Solution:
def findItinerary(self, tickets: List[List[str]]) -> List[str]:
def dfs(curr: str):
while vec[curr]:
tmp = heapq.heappop(vec[curr])
dfs(tmp)
stack.append(curr)
vec = collections.defaultdict(list)
for depart, arrive in tickets:
vec[depart].append(arrive)
for key in vec:
heapq.heapify(vec[key])
stack = list()
dfs("JFK")
return stack[::-1]