反转链表

c++

栈方法

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
            val(x), next(NULL) {
    }
};*/
class Solution {
public:
    ListNode* ReverseList(ListNode* pHead) {
        if(!pHead || !pHead->next) return pHead;
        stack<ListNode*> res;
        ListNode* p = pHead;
        ListNode* newhead;
        while(p->next){
            res.push(p);
            p = p->next;
        }
        //此时p是最后一个结点
        newhead = p;
        while(!res.empty()){
            p->next = res.top();
            p = p->next;
            res.pop();
        }
        //此时p到了反转之后的最后一个结点
        p->next = NULL;
        return newhead;
    }
};

python

指针法

# -*- coding:utf-8 -*-
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class Solution:
    # 返回ListNode
    def ReverseList(self, pHead):
        # write code here
        if pHead==None or pHead.next==None:
            return pHead
        last = None
        cur = pHead
        while cur!=None:
            temp = cur.next
            cur.next = last
            last = cur
            cur = temp
        return last