206翻转链表

使用双指针法，注意一下更新左右指针的顺序就好了。这里还要注意一下终止条件，画个图就行了。leetcode里面头节点就是第一个存储数据的节点，没有虚拟头节点

class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode* left;
        ListNode* right;
        ListNode* temp;
        left = NULL;
        right = head;
        while(right)
        {          
            temp = right->next;
            right->next = left;
            left = right;
            right = temp;
        }
        return left;
    }
};

递归：

class Solution {
public:

    ListNode* MyreversList(ListNode* left, ListNode* right)
    {
        if(right == NULL) return left;
        ListNode* temp;
        temp = right->next;
        right->next = left;
        return MyreversList(right, temp);
    }

    ListNode* reverseList(ListNode* head) {
        return MyreversList(NULL, head);
    }
};