链表合并之一

package LinkTogether;

/*
 * 两个升序链表合并，降序输出，使用栈
 * */

import java.util.Stack;

class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}

public class Demo03 {

    public static void main(String[] args) {
        ListNode n1 = new ListNode(10);            //第一个链表
        ListNode n2 = new ListNode(20);
        ListNode n3 = new ListNode(30);
        ListNode n4 = new ListNode(40);
        n1.next = n2;
        n2.next = n3;
        n3.next = n4;
        
        ListNode n5 = new ListNode(50);            //第二个链表
        ListNode n6 = new ListNode(60);
        ListNode n7 = new ListNode(70);
        ListNode n8 = new ListNode(80);
        n5.next = n6;
        n6.next = n7;
        n7.next = n8;
        
        n1 = Merge(n1,n5);                        //调用合并函数
        
        print(n1);                                //输出
    }
    public static ListNode Merge(ListNode list1,ListNode list2) {
        if(list1 == null && list2 == null)return null;        //如果两个链表都位空，则输出空
        if(list1 == null)return list2;                        //如果链表一为空，则合并后的链表即是链表二
        if(list2 == null)return list1;                        //如果链表二为空，则合并后的链表即是链表三
        Stack<Integer> stk = new Stack<Integer>();            //声明栈
        if(list1.val <= list2.val){                            //链表头部入栈
            stk.push(list1.val);
            stk.push(list2.val);
        }
        if(list1.val > list2.val){
            stk.push(list2.val);
            stk.push(list1.val);
        }
        ListNode temp1 = list1;
        ListNode temp2 = list2;
        while(temp1.next != null || temp2.next != null){
            if(temp1.next != null && temp2.next != null){
                if(temp1.next.val <= temp2.next.val){
                    stk.push(temp1.next.val);
                    stk.push(temp2.next.val);
                }
                if(temp1.next.val >temp2.next.val){
                    stk.push(temp2.next.val);
                    stk.push(temp1.next.val);
                }
            }
            if(temp1.next != null && temp2.next == null){
                stk.push(temp1.next.val);
            }
            if(temp1.next == null && temp2.next != null){
                stk.push(temp2.next.val);
            }
            temp1 = temp1.next;
            temp2 = temp2.next;
        }
        
        int flag = 0;                    //将链表二连在链表一的尾部
        ListNode temp = list1;
        while(flag<2){
            if(temp.next == null){
                flag ++;
                if(flag == 2)break;
                temp.next = list2;
            }
            temp = temp.next;
        }
        
        list1.val = stk.pop();            //取出栈中数据，依次放入链接后的链表中
        temp = list1.next;
        while(!stk.isEmpty()){
               temp.val = stk.pop();
            temp = temp.next;
        }
        return list1;
        
        
    }

    private static void print(ListNode n) {        //输出函数
        System.out.println(n.val);
        if(n.next != null){
            print(n.next);
        }
    }

}