LeetCode重点题系列之【20. Valid Parentheses】

最新推荐文章于 2022-02-10 13:47:19 发布

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本文介绍了一种高效的方法来合并多个已排序的链表成为一个单一的排序链表。通过递归地将链表分成两半并分别进行合并，最终实现了两两合并的功能。这种方法类似于归并排序，但背景是在链表上实现。

Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.

Example:

Input:
[
  1->4->5,
  1->3->4,
  2->6
]
Output: 1->1->2->3->4->4->5->6

This is a hard problem??? Oh, it is! Actually, it's a very good problem, quite like merge sort. But the background is the list, LOL.

class Solution(object):
    def mergeKLists(self, lists):
        """
        :type lists: List[ListNode]
        :rtype: ListNode
        """
        if len(lists)==0:
            return None
        if len(lists)==1:
            return lists[0]
        l1=self.mergeKLists(lists[:len(lists)/2])
        l2=self.mergeKLists(lists[len(lists)/2:])
        return self.mergeTwoList(l1,l2)
    
    
    def mergeTwoList(self,l1,l2):
        dummy=ListNode(0)
        cur=dummy
        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
        if l1:
            cur.next=l1
        if l2:
            cur.next=l2
        return dummy.next