单链表逆序或者逆序输出

分为两种情况，一种是只逆序输出，实际上不逆序；另一种是把链表逆序。

********************逆序输出***********************

#include<iostream>
#include<stack>
#include<assert.h>
using namespace std;

typedef struct node{
int data;
node * next;
}node;

//尾部添加
node * add(int n, node * head){
node * t = new node;
t->data = n;
t->next = NULL;
if (head == NULL){
head = t;
}
else if (head->next == NULL){
head->next = t;
}
else{
node * p = head->next;
while (p->next != NULL){
p = p->next;
}
p->next = t;
}
return head;
}

//顺序输出
void print(node * head){
node * p = head;
while (p != NULL){
cout << p->data << " ";
p = p->next;
}
cout << endl;
}

//递归
void reversePrint(node * p){
if (p != NULL){
reversePrint(p->next);
cout << p->data << " ";
}
}

//栈
void reversePrint2(node * head){
stack<int> s;
while (head != NULL){
s.push(head->data);
head = head->next;
}

while (!s.empty()){
cout << s.top() << " ";
s.pop();
}
}

int main(){

node * head = NULL;
for (int i = 1; i <= 5; i++){
head = add(i, head);
}
print(head);
reversePrint(head);
reversePrint2(head);
system("pause");
return 0;
}

逆序输出可以用三种方法: 递归，栈，逆序后输出。最后一种接下来讲到。

*********************单链表逆序********************

#include<iostream>
#include<stack>
#include<assert.h>
using namespace std;

typedef struct node{
int data;
node * next;
}node;

node * add(int n, node * head){
node * t = new node;
t->data = n;
t->next = NULL;
if (head == NULL){
head = t;
}
else if (head->next == NULL){
head->next = t;
}
else{
node * p = head->next;
while (p->next != NULL){
p = p->next;
}
p->next = t;
}
return head;
}

//循环
node * reverse(node * head){

if (head == NULL || head->next == NULL){
return head;
}

node * p1 = head;
node * p2 = head->next;
node * p3 = NULL;
head->next = NULL;

while (p2 != NULL){
p3 = p2;
p2 = p2->next;
p3->next = p1;
p1 = p3;
}
head = p1;
return head;
}

void print(node * head){
node * p = head;
while (p != NULL){
cout << p->data << " ";
p = p->next;
}
cout << endl;
}

//递归
node * reverse2(node * p){
if (p == NULL || p->next == NULL){
return p;
}

node * newHead = reverse2(p->next);
p->next->next = p;
p->next = NULL;
return newHead;
}

int main(){

node * head = NULL;
for (int i = 1; i <= 5; i++){
head = add(i, head);
}
print(head);
head = reverse(head);
print(head);
head = reverse2(head);
print(head);

system("pause");
return 0;
}

这里链表逆序用了两种方法：循环，递归。理解的方法是在纸上自己画一下。