Solution
from typing import List, Optional
import heapq
class ListNode:
def __init__(self, val=0, next=None):
self.val = val
self.next = next
class Solution:
def mergeKLists(self, lists: List[Optional[ListNode]]) -> Optional[ListNode]:
setattr(ListNode, "__lt__", lambda a, b: a.val < b.val)
pq = [head for head in lists if head]
heapq.heapify(pq)
dummy = cur = ListNode()
while pq:
node = heapq.heappop(pq)
if node.next:
heapq.heappush(pq, node.next)
cur.next = node
cur = cur.next
return dummy.next
# 本地测试工具
def build(arr):
if not arr:
return None
head = ListNode(arr[0])
p = head
for v in arr[1:]:
p.next = ListNode(v)
p = p.next
return head
def show(node):
res = []
while node:
res.append(str(node.val))
node = node.next
print(f"[{','.join(res)}]")
if __name__ == "__main__":
sol = Solution()
lists = [build([1,4,5]), build([1,3,4]), build([2,6])]
show(sol.mergeKLists(lists)) # [1,1,2,3,4,4,5,6]
show(sol.mergeKLists([])) # []
show(sol.mergeKLists([None])) # []