剑指offer-面试题17.合并两个排序的链表

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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.

1 List1:1->3->5->723 List2:2->4->6->84 5 List3:1->2->3->4->5->6->7->8

链表结点定义如下:

1 struct ListNode2 {3     int     m_nValue;4     ListNode* m_pNext;5 }

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:

  1 #include <iostream>  2 using namespace std;  3   4 struct ListNode  5 {  6     int data;  7     struct ListNode *next;  8 };  9  10 struct ListNode* CreateList() 11 { 12     struct ListNode* Head,*p; 13     Head=(struct ListNode*)malloc(sizeof(ListNode)); 14     Head->data=0; 15     Head->next=NULL; 16     p=Head; 17      18     cout<<"Create List....(0-exit!)"<<endl; 19     while(true) 20     { 21         int Data; 22         cin>>Data; 23         if(Data!=0) 24         { 25             struct ListNode* NewNode; 26             NewNode=(struct ListNode*)malloc(sizeof(ListNode)); 27             NewNode->data=Data; 28             NewNode->next=NULL; 29             p->next=NewNode; 30             p=p->next; 31         } 32         else 33         { 34             break; 35         } 36     } 37      38     return Head->next; 39 } 40  41 void PrintList(struct ListNode* Head) 42 { 43     cout<<"The List is: "; 44      45     struct ListNode *p; 46     p=Head; 47     while(p!=NULL) 48     { 49         cout<<p->data<<" "; 50         p=p->next; 51     } 52     cout<<endl; 53 } 54  55 struct ListNode* Merge(ListNode* pHead1,ListNode* pHead2) 56 { 57     if(pHead1==NULL&&pHead2==NULL) 58         return NULL; 59      60     if(pHead1==NULL&&pHead2!=NULL) 61         return pHead2; 62  63     if(pHead1!=NULL&&pHead2==NULL) 64         return pHead1; 65  66     struct ListNode *ptr1,*ptr2,*MergeList,*newhead;; 67      68     ptr1=pHead1; 69     ptr2=pHead2; 70  71     if(ptr1->data>ptr2->data) 72     { 73         MergeList=ptr2; 74         ptr2=ptr2->next; 75     } 76     else 77     { 78         MergeList=ptr1; 79         ptr1=ptr1->next; 80     } 81  82     newhead=MergeList; 83  84     while(ptr1!=NULL&&ptr2!=NULL) 85     { 86         if(ptr1->data>ptr2->data) 87         { 88             MergeList->next=ptr2; 89             ptr2=ptr2->next; 90             MergeList=MergeList->next; 91         } 92          93         if(ptr1->data<ptr2->data) 94         { 95             MergeList->next=ptr1; 96             ptr1=ptr1->next; 97             MergeList=MergeList->next; 98         } 99     }100 101     if(ptr1!=NULL)102     {103         while(ptr1!=NULL)104         {105             MergeList->next=ptr1;106             ptr1=ptr1->next;107             MergeList=MergeList->next;108         }109         MergeList->next=NULL;110     }111     if(ptr2!=NULL)112     {113         while(ptr2!=NULL)114         {115             MergeList->next=ptr2;116             ptr2=ptr2->next;117             MergeList=MergeList->next;118         }119         MergeList->next=NULL;120     }121 122 123     return newhead;124 }125 126 int main()127 {128     ListNode *List1,*List2,*MergeList;129     List1=CreateList();130     PrintList(List1);131     List2=CreateList();132     PrintList(List2);133     MergeList=Merge(List1,List2);134     PrintList(MergeList);135     return 0;136 }

运行截图:

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