合并 k 个排序链表,返回合并后的排序链表。请分析和描述算法的复杂度。
示例:
输入: [ 1->4->5, 1->3->4, 2->6 ] 输出: 1->1->2->3->4->4->5->6
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
class Solution {
public ListNode mergeKLists(ListNode[] lists) {
if (lists.length == 0) return null;
ListNode dumy=new ListNode(0);
int n=lists.length;
while(n>1)
{
int k=(n+1)/2;
for(int i=0;i<n/2;++i)
{
lists[i]= mergeTwoLists(lists[i],lists[i+k]);
}
n=k;
}
return lists[0];
}
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
ListNode dumy=new ListNode(0);
ListNode cur=dumy;
while((l1!=null)&&(l2!=null))
{
if(l1.val<l2.val){
cur.next=l1;
l1=l1.next;
}
else
{
cur.next=l2;
l2=l2.next;
}
cur=cur.next;
}
cur.next=(l1!=null)?l1:l2;
return dumy.next;
}
}