合并k个已排序的链表

二分合并

using System;
using System.Collections.Generic;

/*
public class ListNode
{
    public int val;
    public ListNode next;

    public ListNode (int x)
    {
        val = x;
    }
}
*/

class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param lists ListNode类一维数组 
     * @return ListNode类
     */
    public ListNode mergeKLists (List<ListNode> lists) {
        // write code here
        if(lists==null||lists.Count==0)
        {
            return null;
        }
        int len = lists.Count;
        while(len>1){
            for(int i=0; i<len/2; i++){
                lists[i] = mergeNode(lists[i],lists[len-1-i]);
            }
            len = len-len/2;
        }
        return lists[0];
    }
    public ListNode mergeNode (ListNode listNode1, ListNode listNode2) {
        if(listNode1 == null && listNode2 == null)
        {
            return null;
        }
        ListNode vhead = new ListNode(-1);
        ListNode curr = vhead;
        while(listNode1 != null && listNode2 != null){
            if(listNode1.val<listNode2.val){
                curr.next = listNode1;
                curr = listNode1;
                listNode1 = listNode1.next;
            }
            else{
                curr.next = listNode2;
                curr = listNode2;
                listNode2 = listNode2.next;
            }
        }
        if(listNode1 != null){
            curr.next = listNode1;
        }
        else if(listNode2 != null){
            curr.next = listNode2;
        }

        return vhead.next;
        // write code here
    }
}