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.

1 List1:1->3->5->7

2

3 List2:2->4->6->8

4 

5 List3:1->2->3->4->5->6->7->8

链表结点定义如下:

1 struct ListNode

2 {

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: