Leetcode23--->Merge K sorted Lists(合并k个排序的单链表)

 1 /**
 2  * Definition for singly-linked list.
 3  * public class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int x) { val = x; }
 7  * }
 8  */
 9 public class Solution {
10     public ListNode mergeKLists(ListNode[] lists) {
11         if(lists == null|| lists.length == 0)
12             return null;
13         if(lists.length == 1)
14             return lists[0];
15         int end = lists.length - 1;
16         int begin = 0;
17         while(end > 0)  // 将lists的头和尾进行归并，然后将结果存放在头，头向后移动，尾向前移动，直到begin=end,则已经归并了一半，此时将begin=0,继续归并
18         {
19             begin = 0;
20             while(begin < end)
21             {
22                 lists[begin] = combineTwoList(lists[begin], lists[end]);
23                 begin ++;
24                 end --;
25             }
26         }
27 
28         return lists[0];
29     }
30     public ListNode combineTwoList(ListNode head1, ListNode head2) // head1和head2为头节点的两个单链表的合并
31     {
32         if(head1 == null && head2 == null) // 如果两个单链表都不存在，则返回null
33             return null;
34         if(head1 == null)  // 如果head1不存在，则直接返回head2
35             return head2;
36         if(head2 == null)
37             return head1;
38         ListNode pHead = null;
39         if(head1.val > head2.val) // 根据head1与head2的值，决定头节点
40         {
41             pHead = head2;
42             pHead.next = combineTwoList(head1, head2.next);
43         }
44         else
45         {
46              pHead = head1;
47              pHead.next = combineTwoList(head1.next, head2);
48         }
49         return pHead;
50     }
51 }