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
        return divdeMearge(0,lists.size()-1,lists);
    }

    protected ListNode divdeMearge(int left,int right,ArrayList<ListNode> lists){
        if(left> right) return null;
        if(left==right){
            return lists.get(left);
        }
        int mid=(left+right)/2;

        return merge(divdeMearge(left,mid,lists),divdeMearge(mid+1,right,lists));
    }

    protected ListNode merge(ListNode leftlist,ListNode rightlist){
        if(leftlist==null) return rightlist;
        if(rightlist==null) return leftlist;
        ListNode dummpy=new ListNode(0);
        ListNode res=dummpy;

        while(leftlist!=null&&rightlist!=null){
            if(leftlist.val<rightlist.val){
                dummpy.next=leftlist;
                leftlist=leftlist.next;
            }
            else{
                dummpy.next=rightlist;
                rightlist=rightlist.next;
            }
            dummpy=dummpy.next;
        }
        if(leftlist==null) dummpy.next=rightlist;
        if(rightlist==null) dummpy.next=leftlist;
        return res.next;

    }
}