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) {
        // write code here
	   //判断是否有链表为空
        if (pHead1 == null) {
            return pHead2;
        }
        if (pHead2 == null) {
            return pHead1;
        }
        if (pHead1 == null && pHead2 == null ) {
            return null;
        }
        //两个链表都不为空
        ListNode node1 = pHead1;
        ListNode node2 = pHead2;
        ListNode newHead = null;
        //确定头节点
        if (node1 != null && node2 != null && node1.val <= node2.val) {
            newHead = node1;
            node1 = node1.next;
        }
        else{
            newHead = node2;
            node2 = node2.next;
        }
        //创建临时节点 
        ListNode temp = newHead;
        //
        while (node1 != null && node2 != null) {
            if (node1.val <= node2.val) {
                temp.next = node1;
                node1 = node1.next;
            } else {
                temp.next = node2;
                node2 = node2.next;
            }
            temp = temp.next;
        }
        //走到一个链表的末尾时 将另一个链表的剩余部分直接连起来
        if (node1 == null) {
            temp.next = node2;
        }
        if (node2 == null) {
            temp.next = node1;
        }
        return newHead;
    }
}