https://leetcode-cn.com/problems/reverse-linked-list/

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/**
 * 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 * pre = NULL;
        ListNode * cur = head;
        ListNode * next = NULL;
        while(cur != NULL) {
            next = cur -> next;
            cur -> next = pre;
            //next -> next = cur;
            pre = cur;
            cur = next;
        }
        return pre;
    }
};