剑指offer-面试题17.合并两个排序的链表

题目:输入两个递增的排序的链表,合并这两个链表并使新链表中的节点仍然是

按照递增排序的。例如链表1链表2合并为链表3.

 List1:->->->

 List2:->->->

 List3:->->->->->->->

链表结点定义如下:

 struct ListNode
 {
     int     m_nValue;
     ListNode* m_pNext;
 }

其实我们可以简单梳理下流程如下:

1.两个指针分别指向List1和List2的头结点。设为ptr1和ptr2

2.比较ptr1和ptr2结点的值,ptr1<ptr2则ptr1则是合并后的链表头结点

3.ptr1向后移动一个结点此时再比较 ptr1>ptr2则将ptr2的节点插入到头结点之后

4.当ptr1或者ptr2到达末尾时 比如ptr1到达List1结尾后 若此时ptr2还未到List2结尾

   将ptr2插入到新排序的链表后面.

代码实现如下:

 #include <iostream>
 using namespace std;

 struct ListNode
 {
     int data;
     struct ListNode *next;
 };

 struct ListNode* CreateList()
 {
     struct ListNode* Head,*p;
     Head=(struct ListNode*)malloc(sizeof(ListNode));
     Head->data=;
     Head->next=NULL;
     p=Head;

     cout<<"Create List....(0-exit!)"<<endl;
     while(true)
     {
         int Data;
         cin>>Data;
         if(Data!=)
         {
             struct ListNode* NewNode;
             NewNode=(struct ListNode*)malloc(sizeof(ListNode));
             NewNode->data=Data;
             NewNode->next=NULL;
             p->next=NewNode;
             p=p->next;
         }
         else
         {
             break;
         }
     }

     return Head->next;
 }

 void PrintList(struct ListNode* Head)
 {
     cout<<"The List is: ";

     struct ListNode *p;
     p=Head;
     while(p!=NULL)
     {
         cout<<p->data<<" ";
         p=p->next;
     }
     cout<<endl;
 }

 struct ListNode* Merge(ListNode* pHead1,ListNode* pHead2)
 {
     if(pHead1==NULL&&pHead2==NULL)
         return NULL;

     if(pHead1==NULL&&pHead2!=NULL)
         return pHead2;

     if(pHead1!=NULL&&pHead2==NULL)
         return pHead1;

     struct ListNode *ptr1,*ptr2,*MergeList,*newhead;;

     ptr1=pHead1;
     ptr2=pHead2;

     if(ptr1->data>ptr2->data)
     {
         MergeList=ptr2;
         ptr2=ptr2->next;
     }
     else
     {
         MergeList=ptr1;
         ptr1=ptr1->next;
     }

     newhead=MergeList;

     while(ptr1!=NULL&&ptr2!=NULL)
     {
         if(ptr1->data>ptr2->data)
         {
             MergeList->next=ptr2;
             ptr2=ptr2->next;
             MergeList=MergeList->next;
         }

         if(ptr1->data<ptr2->data)
         {
             MergeList->next=ptr1;
             ptr1=ptr1->next;
             MergeList=MergeList->next;
         }
     }

     if(ptr1!=NULL)
     {
         while(ptr1!=NULL)
         {
             MergeList->next=ptr1;
             ptr1=ptr1->next;
             MergeList=MergeList->next;
         }
         MergeList->next=NULL;
     }
     if(ptr2!=NULL)
     {
         while(ptr2!=NULL)
         {
             MergeList->next=ptr2;
             ptr2=ptr2->next;
             MergeList=MergeList->next;
         }
         MergeList->next=NULL;
     }

     return newhead;
 }

 int main()
 {
     ListNode *List1,*List2,*MergeList;
     List1=CreateList();
     PrintList(List1);
     List2=CreateList();
     PrintList(List2);
     MergeList=Merge(List1,List2);
     PrintList(MergeList);
     return ;
 }

运行截图: