[C topic] Li Kou 206. reverse the linked list

206. Reverse a linked list - Power button （LeetCode）

  Method 1 ： Create a new list , Its head node newhead At the beginning of NULL, Traverse the old linked list , If the node is not NULL, Insert its head into the new linked list . Insert once at each end ,newhead Just update it once （ By cur assignment ）.

struct ListNode* reverseList(struct ListNode* head)
{
    struct ListNode* cur=head;
    struct ListNode* newhead=NULL;// Create a new head node , Traverse the old list , Insert it head ,NULL It will become the point of the tail node 
    while(cur)
    {
        struct ListNode* tmp=cur->next;
        cur->next=newhead;
        newhead=cur;// to update newhead
        cur=tmp;// Check the next node of the old linked list 
    }
    return newhead;
}

Method 2 ： Turn the pointer to the direction of the target .（ I feel that the previous method is better ）

struct ListNode* reverseList(struct ListNode* head)
{
    struct ListNode* cur=head;// Mark the current node 
    struct ListNode* aim=NULL;// Will be cur Pointed node 
    if(cur==NULL)
        return NULL;
    while(cur->next!=NULL)// If there is a node behind the current node in the old linked list , take cur Move back one node , Re change cur The direction of .
    {
        struct ListNode* tmp=cur->next;
        cur->next=aim;
        aim=cur;
        cur=tmp;
    }
    cur->next=aim;
    return cur;
}