题解 | #合并两个排序的链表#

1. 画图
2. 设置虚拟头结点

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 pHead1 ListNode类 
     * @param pHead2 ListNode类 
     * @return ListNode类
     */
    public ListNode Merge (ListNode pHead1, ListNode pHead2) {
        // write code here
        ListNode dummynode  = new ListNode(-1);

        dummynode.next = pHead1;
        ListNode pre = dummynode;
        while(pHead1!=null &&pHead2 !=null)
        {
            if(pHead2.val < pHead1.val )
            {
                ListNode next = pHead2.next;

                pHead2.next = pHead1;
                pre.next = pHead2;
                pHead2 = next;
                pre = pre.next;
            }else{
                pre = pHead1;
                pHead1 = pHead1.next;
                
            }
        }

        if(pHead1 ==null)
        {
            pre.next = pHead2;
        }

        return dummynode.next;


    }
}