1 #include <iostream>
  2 #include <malloc.h>
  3 using namespace std;
  4 struct ListNode {
  5      int val;
  6      ListNode *next;
  7      ListNode(int x) : val(x), next(NULL) {}
  8  };
  9  /*-----------------------------创建链表(不带头结点)---------------------------------*/
 10 /*在链表的末端插入新的节点，建立链表*/
 11 ListNode *CreateList(int n)
 12 {
 13     ListNode *head;//指向头结点指针
 14     ListNode *p,*pre;
 15     int i;
 16     head=(ListNode *)malloc(sizeof(ListNode));//为头节点分配内存空间
 17     head->next=NULL;//将头结点的指针域清空
 18     pre=head;//先将头结点首地址赋给中间变量pre
 19     for(i=1;i<=n;i++)//通过for循环不断加入新的结点
 20     {
 21         p=(ListNode *)malloc(sizeof(ListNode));//为要插入的节点分配
 22         //内存空间p指向新插入结点的首地址
 23         cin>>p->val;//输入数值
 24         pre->next=p;//将p指向新结点插入链表也就是头结点指针域指向
 25         //下个结点
 26         //第一个结点就是p指向的，因为头结点内容为空
 27         pre=p;//这个起着指向下一个结点的作用  等价于pre=pre->next
 28     }
 29     p->next=NULL;//最后将最后一个结点的指针域清空了
 30 
 31     return head->next;//不带空的头结点
 32 }
 33 /*-------------------------输出链表-----------------------------------*/
 34 void PrintList(ListNode *h)
 35 {
 36     ListNode *p;
 37 
 38     p=h;//不带空的头结点
 39     while(p)
 40     {
 41         cout<<p->val<<" ";
 42         p=p->next;
 43         cout<<endl;
 44     }
 45 }
 46 class Solution {
 47 public:
 48     ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
 49         int n1 = 0;
 50         int n2 = 0;
 51         ListNode * head = new ListNode(0);
 52         ListNode * ptr = head;
 53         ListNode *l = l1;
 54         while(l1 != NULL && l2 != NULL)
 55         {
 56             if(l1->val <= l2->val)
 57             {
 58                 l = l1;
 59                 l1 = l1->next;
 60 
 61             }
 62             else
 63             {
 64                 l = l2;
 65                 l2 = l2->next;
 66             }
 67             ptr->next = l;
 68             ptr = ptr->next;
 69         }
 70         while(l1 != NULL)
 71         {
 72             l = l1;
 73             l1 = l1->next;
 74             ptr->next = l;
 75             ptr = ptr->next;
 76         }
 77         while(l2 != NULL)
 78         {
 79             l = l2;
 80             l2 = l2->next;
 81             ptr->next = l;
 82             ptr = ptr->next;
 83         }
 84         return head->next;
 85     }
 86 };
 87 int main()
 88 {
 89     int n1;
 90     int n2;
 91     ListNode *h1;
 92     ListNode *h2;
 93     ListNode *h;
 94     cout<<"输入链表1的结点数目"<<endl;
 95     cin>>n1;
 96     h1 = CreateList(n1);
 97     cout<<"链表1为："<<endl;
 98     PrintList(h1);
 99     cout<<"输入链表2的结点数目"<<endl;
100     cin>>n2;
101     h2 = CreateList(n2);
102     cout<<"链表2为："<<endl;
103     PrintList(h2);
104     Solution s;
105     h = s.mergeTwoLists(h1,h2);
106     cout<<"合并后链表为: "<<endl;
107     PrintList(h);
108 
109     return 0;
110 }