leetcode:Reverse Linked List

Reverse a singly linked list.

/**
 * Definition for singly-linked list.
 * struct ListNode {
 * int val;
 * ListNode *next;
 * ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode *s,*p,*l=NULL;

        p=head;
        if(p == NULL || p->next ==NULL) return head;

        while(p->next!=NULL)
        {
            s=p->next;
            p->next = l;
            l=p;
            p=s;
        }

        p->next = l;

        head=p;
        return head;
    }
};