从头打印链表

三指针法

/*
struct ListNode {
	int val;
	struct ListNode *next;
	ListNode(int x) :
			val(x), next(NULL) {
	}
};*/
class Solution {
public:
    ListNode* ReverseList(ListNode* pHead) {
        ListNode* pre = NULL, *cur = pHead,*next  = pHead;
        while(cur){
        next = cur->next;
        cur->next = pre;
        pre = cur;
        cur = next;
        }
        return pre;
    }
};