leetcode 23 合并 k 个有序链表

Posted 2021-12-19 dogelife

问题描述

* leetcode 23，  Merge k Sorted Lists

解题思路

1. 合并2个有序链表的进阶版，很容易想到，利用分治进行处理。

   把个数大于2的集合 两两划分处理，最后再做最后一步的处理。

    1 public class Solution 
    2     public ListNode mergeKLists(ListNode[] lists) 
    3         if (lists.length==0 || lists==null)  return null; 
    4         return merge(lists, 0, lists.length-1);
    5     
    6     public static ListNode merge(ListNode[] lists, int left, int right) 
    7         if (left == right)  return lists[left]; 
    8         int mid = left + (right-left)/2;
    9         ListNode l1 = merge(lists, left, mid);
   10         ListNode l2 = merge(lists, mid+1, right);
   11         return merger2Lists(l1, l2);
   12     
   13     public static ListNode merger2Lists(ListNode l1, ListNode l2) 
   14         // 递归写法
   15         if (l1==null)  return l2; 
   16         if (l2==null)  return l1; 
   17         ListNode head = null;
   18         if (l1.val < l2.val) 
   19             head = l1;
   20             head.next = merger2Lists(l1.next, l2);
   21          else 
   22             head = l2;
   23             head.next = merger2Lists(l1, l2.next);
   24         
   25         return head;
   26     
   27 
   28