题解 | 合并k个已排序的链表

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public 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ArrayList 
     * @return ListNode类
     */
    public ListNode mergeKLists (ArrayList<ListNode> lists) {
        // write code here
            if(lists==null || lists.size()==0){
                return null;
            }
            if(lists.size()==1){
                return lists.get(0);
            }
            //合并两个
            ListNode n1=lists.get(0);
            ListNode n2=lists.get(1);
            ListNode result=merge(n1,n2);
            for(int i=2;i<lists.size();i++){
                result=merge(result,lists.get(i));
            }
        return result;

    }

    private ListNode merge(ListNode n1, ListNode n2){
            if(n1==null|| n2==null){
                return n1!=null?n1:n2;
            }
            if(n1.val<=n2.val){
                n1.next=merge(n1.next,n2);
                return n1;
            }else{
                n2.next=merge(n2.next,n1);
                return n2;
            }
    }








}