leetcode 206. Reverse 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 * before = NULL;
        ListNode * next;
        while(head != NULL){
            next = head->next;
            head->next = before;
            before = head;
            head = next;
        }
        return before;
    }
};