题解 | #合并两个排序的链表#

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 pHead1 ListNode类 
     * @param pHead2 ListNode类 
     * @return ListNode类
     */
    public ListNode Merge (ListNode pHead1, ListNode pHead2) {
        //先判断是否有为空的链表，一一进行返回
        if(pHead1==null){
            return pHead2;
        }
        if(pHead2==null){
            return pHead1;
        }
        if(pHead1==null&&pHead2==null){
            return null;
        }
        //创建一个pHead3链表来存pHead1，pHead2链表
        ListNode phead3 =new ListNode(0);
        //给phead3创建一个当前指针
        ListNode cur=phead3;
        //将pHead1、pHead2插入到phead3中
        while(true){
            //如果pHead1链表空了，那么将pHead2连到phead3尾部，此时完成合并，返回phead3
            if(pHead1==null){
                cur.next=pHead2;
                return phead3.next;
            }
            //如果pHead2链表空了，那么将pHead1连到phead3尾部，此时完成合并，返回phead3
            if(pHead2==null){
                cur.next=pHead1;
                return phead3.next;
            }
            //如果pHead1.val<=pHead2.val,则将pHead1当前节点连到pHead3尾部，pHead1指针后移
            if(pHead1.val<=pHead2.val){
                cur.next=pHead1;
                pHead1=pHead1.next;
            }else{
                cur.next=pHead2;
                pHead2=pHead2.next;
            }
            cur=cur.next;
        }
    }
}