23. Merge k Sorted Lists

Leetcode: 23. Merge k Sorted Lists
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

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode mergeKLists(ListNode[] lists) {
        int len=lists.length;
        
        if(lists==null||len==0) return null;
        if(len==1) return lists[0];
        
        while(len>1)//基于“二分”思想进行链表的两两组合
        {
            int mid=(len+1)/2;//二分
            for(int i=0;i