迭代法：
/** * 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) { if(!head || !head->next) return head; ListNode *pre=NULL, *p=head, *next=NULL; while(p){ next=p->next; p->next=pre; pre=p; p=next; } return pre; } };