反转链表

输入一个链表，反转链表后，输出链表的所有元素。

我的代码：

class Solution {
public:
    ListNode* ReverseList(ListNode* pHead) {
        if(pHead == NULL)
            return NULL;
        stack<ListNode*> sta;
        while(pHead != NULL)
        {
            sta.push(pHead);
            pHead = pHead->next;
        }
        ListNode* p = sta.top();
        ListNode* pp = sta.top();
        while(!sta.empty())
        {
            p = sta.top();
            sta.pop();
            if(!sta.empty())
                p->next = sta.top();
            else 
                p->next = NULL;
        }
        return pp;
    }
};

 

小黑的代码：

class Solution {
    public:
        ListNode* ReverseList(ListNode* pHead) {
            if(pHead == NULL)
                return NULL;
            stack<ListNode*> sta;
            while(pHead != NULL)
            {
                sta.push(pHead);
                pHead = pHead->next;
            }
            ListNode* p = sta.top();
            ListNode* pp = sta.top();//记录链表的头
            sta.pop();
            while(!sta.empty())
            {
                p->next = sta.top();
                sta.pop();
                p=p->next;
            }
            p -> next = NULL;
            return pp;
        }
};

 3个指针代码：

Node* Reverse(Node* node)
{
    Node* pre = node;
    Node* p = node->next;
    Node* pnxt = p->next;
    node->next = NULL;
    while(pnxt != NULL)
    {
        p->next = pre;
        pre = p;
        p = pnxt;
        pnxt = pnxt->next;
    }
    p->next = pre;
    return p;
}

 

改进版：

Node* Reverse(Node* node)
{
    Node* pre = NULL;//被指向的
    Node* p = node;//当前
    Node* pnxt = node->next;//要断开的
    while(pnxt != NULL)
    {
        p->next = pre;
        pre = p;
        p = pnxt;
        pnxt = pnxt->next;
    }
    p->next = pre;
    return p;
}