【LC23】合并K个有序链表

class Solution:
    def mergeKLists(self, lists: List[ListNode]) -> ListNode:
        n = len(lists)
        if n == 0: return None
        if n == 1: return lists[0]
        
        mid = n // 2
        return self.mergeTwoLists(self.mergeKLists(lists[:mid]), self.mergeKLists(lists[mid:]))
    
    # 迭代写法 
    def mergeTwoLists(self, node1, node2):
        dummy = cur = ListNode()
        while node1 and node2:
            if node1.val <= node2.val:
                cur.next = node1
                node1 = node1.next
            else:
                cur.next = node2
                node2 = node2.next
            cur = cur.next

        cur.next = node1 if node1 else node2
        return dummy.next