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) {
        // 双链表一一比较
	  //链表皆空，则返回空链表
        if (pHead1 == null && pHead2 == null) return pHead1;
	  //哨兵节点
        ListNode ret = new ListNode(-1);
        ListNode temp = ret;
	  //循环到一方链表为空
        while (pHead1 != null && pHead2 != null) {
            if (pHead1.val <= pHead2.val) {
                temp.next = pHead1;
                temp = temp.next;
                pHead1 = pHead1.next;
            } else {
                temp.next = pHead2;
                temp = temp.next;
                pHead2 = pHead2.next;
            }
        }
	  //循环结束，一链表到链尾，把temp指向另一链表剩下的节点
        if (pHead1 == null) {
            temp.next = pHead2;
            return ret.next;
        } else if (pHead2 == null) {
            temp.next = pHead1;
            return ret.next;
        }
        return ret.next;
    }
}