无结点单链表反转

两种方法：新建链表头插法和就地反转法

#include<iostream>
using namespace std;


struct ListNode {
    int val;
    ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};

//新建链表头插法
ListNode* reverseList(ListNode* head) {
    if (head == NULL)
        return head;
    ListNode* p=NULL;
    ListNode* pCur = head;
    while (pCur != NULL)
    {
        ListNode* newNode = new ListNode(pCur->val);
        newNode->next = p;
        p = newNode;
        pCur = pCur->next;
    }
    return p;
}

//就地反转法
ListNode* reverseList1(ListNode* head)
{
    if (head == NULL || head->next == NULL)
        return head;
    ListNode* pre = head;
    ListNode* pCur = head->next;
    while (pCur!=NULL)
    {
        pre->next = pCur->next;
        pCur->next = head;
        head = pCur;
        pCur = pre->next;
    }
    return head;
}

int main()
{
    ListNode* head=new ListNode(0);
    ListNode* node1 = new ListNode(1);
    ListNode* node2 = new ListNode(2);
    ListNode* node3 = new ListNode(3);
    ListNode* node4 = new ListNode(4);
    ListNode* node5 = new ListNode(5);
    head->next = node1;
    node1->next = node2;
    node2->next = node3;
    node3->next = node4;
    node4->next = node5;
    node5->next = NULL;

    ListNode* pCurrent = head;
    while (pCurrent != NULL)
    {
        cout << pCurrent->val << " ";
        pCurrent = pCurrent->next;
    }
    cout << endl << endl;

    ListNode* node= reverseList1(head);

    ListNode* pCurrent1 = node;
    while (pCurrent1 != NULL)
    {
        cout << pCurrent1->val << " ";
        pCurrent1 = pCurrent1->next;
    }
    cout << endl << endl;

    return 0;
}