python leetcode 23. Merge k Sorted Lists

Merge two Sorted Lists的进阶版

建立Merge two Sorted Lists函数 合并两个链表，mergeKLists中不断二分再合并

class Solution(object):
    def mergeKLists(self, lists):
        """
        :type lists: List[ListNode]
        :rtype: ListNode
        """
        if not lists:
            return None
        if len(lists) == 1:
            return lists[0]
        l1 = self.mergeKLists(lists[:len(lists)//2])
        l2 = self.mergeKLists(lists[len(lists)//2:])
        head = self.mergeTwoLists(l1,l2)
        return head
    def mergeTwoLists(self, l1, l2):
        if not l1 and not l2:
            return None 
        if not l1:
            return l2 
        if not l2:
            return l1 
        p = ListNode(0)
        res = p 
        while l1 and l2:
            if l1.val < l2.val:
                p.next = l1 
                l1=l1.next 
                p = p.next
            else:
                p.next = l2 
                l2 = l2.next
                p = p.next 
        if l1:
            p.next=l1 
        if l2:
            p.next=l2
        return res.next