链表的反转操作

思路很简单，每次取两个结点，使后一个结点指向前一个结点，再用一个变量保存后面剩余的链表，每次移动一位，最后把剩下的两个连起来，但是很容易错，next指针很难弄清楚。

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#pragma warning(disable:4996)
#include<iostream>
#include<cstring>
#include<cstdio>
#include<climits>
#include<algorithm>
#include<vector>
#include<queue>
#include<set>
using namespace std;
typedef long long ll;
typedef int datatype;
struct node
{
	datatype info;
	struct node* next;
};
node* init()
{
	return NULL; 
}
//头插法
node* insert_head(node* head, int x)
{
	node* p;
	p = (node*)malloc(sizeof(node));
	p->info = x;
	p->next = head;
	head = p;
	return head;
}
//尾插法
node* insert_tail(node* head, int n)
{
	int i, t;
	head = (node*)malloc(sizeof(node));
	node* end, * temp;
	end = head;
	for (i = 0;i < n;i++)
	{
		temp = (node*)malloc(sizeof(node));
		scanf("%d", &t);
		temp->info = t;
		end->next = temp;
		end = temp;
	}
	end->next = NULL;
	return head->next;
}
void display(node* head)
{
	node* p = head;
	if (p == NULL)
	{
		printf("链表是空的\n");
		return;
	}
	while (p)
	{
		printf("%d ", p->info);
		p = p->next;
	}
	printf("\n");
}
node* reverse(node* head)
{
	if (head == NULL)
	{
		printf("链表是空的\n");
		return NULL;
	}
	node* p, * q = head, * r;
	p = q->next;r = p->next;
	//q代表第一个结点，p代表第二个，r代表剩下的链表
	q->next = NULL;
	while (r)
	{
		//p->next = NULL;表示和剩下的链表断裂，不加这句也可以	
		p->next = q;//连接到q上
		q = p;
		p = r;
		r = r->next;//后移一位，顺序很重要
	}
	p->next = q;//把最后剩下的连起来
	return p;
}
int main()
{
	int n, i, j, val, x, y;
	node* head = NULL;
	printf("输入结点个数：");
	scanf("%d", &n);
	head = insert_tail(head, n);
	printf("链表从头到尾：");
	display(head);
	head = reverse(head);
	printf("逆转后：");
	display(head);
	return 0;
}

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