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.isEmpty())
        {
            return null;
        }
        ListNode s = lists.get(0);
        for(int i = 1; i < lists.size();i++){
            s = merge(s,lists.get(i));
        }
       return s;
    }
    public ListNode merge(ListNode list1, ListNode list2){
      if(list1 == null){
        return list2;
      }
      if(list2 == null){
        return list1;
      }
     if(list1.val<=list2.val){
                list1.next = merge(list1.next,list2);
                return list1;
        }else{
                list2.next = merge(list1,list2.next);
                return list2;
            }
    }








}