【Turn】The turn of the linked list

The turn of the linked list is often tested, and there are many methods.

I saw one of the most intuitive and easy-to-understand ones on the Internet today, and excerpted them for your reference.

Reprinted from: http://blog.csdn.net/feliciafay/article/details/6841115

 

Method: Use 3 pointers to traverse the singly linked list, and reverse the link points one by one.

Steps: Use the two pointers p and q to work together to make the points between the two nodes reverse, and use r to record the remaining linked list.

p = head;

q = head->next;

 head->next = NULL;

 Now enter the body of the loop, which is the first loop.

r = q->next;

q->next = p;

p = q

q =r;

Second cycle.

r = q->next

 q->next = p;  

p = q

q = r

 The third cycle. . . . .

 

code show as below:

ActList* ReverseList2(ActList* head)  
{  
    //ActList* temp=new ActList;  
 if(NULL==head|| NULL==head->next) return head; //There is no need to reverse if there are less than two nodes.  
    ActList* p;  
    ActList* q;  
    ActList* r;  
    p = head;    
    q = head->next;  
    head->next = NULL; //The old head pointer is the new tail pointer, next needs to point to NULL  
    while(q){  
        r = q->next; //First keep the pointer to be processed by the next step  
        q->next = p; //Then pq works alternately for reverse  
        p = q   
        q = r;   
    }  
    head=p; // Finally q must point to NULL, so p is returned as the new head pointer  
    return head;      
}