Leetcode 23. Merge k Sorted Lists（python）

分治法两两合并，才没有超时

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    
    def mergeKLists(self, lists):
        """
        :type lists: List[ListNode]
        :rtype: ListNode
        """
        if len(lists)==0:   return []
        return self.merge(lists,0,len(lists)-1)
    
    def merge(self,lists,l,r):
        if l<r:
            mid=(l+r)/2
            return self.mergeTwoLists(self.merge(lists,l,mid),self.merge(lists,mid+1,r))
        return lists[l]
        
        
    def mergeTwoLists(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        res=cur=ListNode(0)
        
        while l1 and l2:
            if l1.val<l2.val:
                cur.next=l1
                l1=l1.next
            else:
                cur.next=l2
                l2=l2.next
            cur=cur.next
        cur.next=l1 or l2
        return res.next