# Definition for singly-linked list.
# class ListNode:
# def __init__(self, val=0, next=None):
# self.val = val
# self.next = next
class Solution:
def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
dummy =ListNode()
tail =dummy
while list1 and list2 :
if list1.val <= list2.val :
tail.next =list1
list1=list1.next
else:
tail.next =list2
list2 =list2.next
tail= tail.next
if list1:
tail.next =list1
elif list2:
tail.next=list2
return dummy.next
def mergeKLists(self, lists: List[Optional[ListNode]]) -> Optional[ListNode]:
if not lists:
return None
while len(lists)>1:
temp_node_list =[]
for i in range(0,len(lists),2):
list_Node1=lists[i]
list_Node2 = lists[i+1] if i+1<len(lists) else None
temp_node_list.append(self.mergeTwoLists(list_Node1,list_Node2))
lists =temp_node_list
return lists[0]