剑指offer-面试题24-反转链表-链表

/*
题目：
	定义一个函数，输入链表的头结点，反转链表输出反转后链表的头节点。
*/
/*
思路：
	记录当前节点的next和pre。
	断开当前节点指向next的指针，指向pre。
*/
#include <iostream>
#include<cstdlib>

using namespace std;

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

ListNode* ReverseList(ListNode* pHead) {
    if(pHead == nullptr || pHead->next == nullptr) return pHead;

    ListNode* pre = pHead;
    ListNode* curr = pHead->next;
    pre->next = nullptr;
    ListNode* next = nullptr;
    while(curr){
        next = curr->next;
        curr->next =pre;
        pre = curr;
        curr = next;
    }
    return pre;
}

int main()
{
    ListNode *node6 = new ListNode(6);
    ListNode *node5 = new ListNode(5);
    ListNode *node4 = new ListNode(4);
    ListNode *node3 = new ListNode(3);
    ListNode *node2 = new ListNode(2);
    ListNode *node1 = new ListNode(1);
    ListNode *pHead = new ListNode(0);
    pHead->next = node1;
    node1->next = node2;
    node2->next = node3;
    node3->next = node4;
    node4->next = node5;
    node5->next = node6;
    node6->next = nullptr;

    pHead = ReverseList(pHead);
    cout<<"answer"<<endl;
    while(pHead != nullptr){
        cout<<pHead->val<<endl;
        pHead = pHead->next;
    }

    cout << "Hello world!" << endl;
    return 0;
}