The sword refers to the offer---- reverse the linked list

/*
struct ListNode {
	int val;
	struct ListNode *next;
	ListNode(int x) :
			val(x), next(NULL) {
	}
};*/
// recursive version
class Solution1 {
public:
    ListNode* ReverseList(ListNode* pHead) {
        if (pHead == NULL || pHead-> next == NULL)
            return pHead;
        ListNode * p  = ReverseList(pHead->next);
        pHead-> next-> next = pHead;
        pHead->next = NULL;
        return p;//Only return the last node
    }
};

// non-recursive version
class Solution {
public:
    ListNode* ReverseList(ListNode* pHead) {
        if (pHead == NULL || pHead-> next == NULL)
            return pHead;
        ListNode * pre = pHead;
        ListNode * last  = NULL;
        ListNode * next  = NULL;
        while(pre != NULL)
        {
            next = pre->next;
            pre->next = last;
            last = pre;
            pre = next;
        }
        return last;
    }
};