如何仅使用两个指针反转单链表?
-
05-07-2019 - |
题
我想知道是否存在一些逻辑来仅使用两个指针来反转链表。
以下用于使用三个指针反转单个链表: p
, q
, r
:
struct node {
int data;
struct node *link;
};
void reverse() {
struct node *p = first,
*q = NULL,
*r;
while (p != NULL) {
r = q;
q = p;
p = p->link;
q->link = r;
}
first = q;
}
还有其他替代方法可以反转链表吗?在时间复杂度方面,逆转单链表的最佳逻辑是什么?
解决方案
任何替代方案?不,这很简单,并没有根本不同的方式。这个算法已经是O(n)时间了,你不能比这更快,因为你必须修改每个节点。
看起来您的代码在正确的轨道上,但它在上面的表单中并不完全正常。这是一个工作版本:
#include <stdio.h>
typedef struct Node {
char data;
struct Node* next;
} Node;
void print_list(Node* root) {
while (root) {
printf("%c ", root->data);
root = root->next;
}
printf("\n");
}
Node* reverse(Node* root) {
Node* new_root = 0;
while (root) {
Node* next = root->next;
root->next = new_root;
new_root = root;
root = next;
}
return new_root;
}
int main() {
Node d = { 'd', 0 };
Node c = { 'c', &d };
Node b = { 'b', &c };
Node a = { 'a', &b };
Node* root = &a;
print_list(root);
root = reverse(root);
print_list(root);
return 0;
}
其他提示
我不想成为坏消息的承载者,但我不认为你的三指针解决方案确实有效。当我在以下测试工具中使用它时,列表减少到一个节点,按照以下输出:
==========
4
3
2
1
0
==========
4
==========
你不会比你的解决方案获得更好的时间复杂度,因为它是O(n)并且你必须访问每个节点来改变指针,但你可以做一个只有两个额外指针的解决方案很容易,如下面的代码所示:
#include <stdio.h>
// The list element type and head.
struct node {
int data;
struct node *link;
};
static struct node *first = NULL;
// A reverse function which uses only two extra pointers.
void reverse() {
// curNode traverses the list, first is reset to empty list.
struct node *curNode = first, *nxtNode;
first = NULL;
// Until no more in list, insert current before first and advance.
while (curNode != NULL) {
// Need to save next node since we're changing the current.
nxtNode = curNode->link;
// Insert at start of new list.
curNode->link = first;
first = curNode;
// Advance to next.
curNode = nxtNode;
}
}
// Code to dump the current list.
static void dumpNodes() {
struct node *curNode = first;
printf ("==========\n");
while (curNode != NULL) {
printf ("%d\n", curNode->data);
curNode = curNode->link;
}
}
// Test harness main program.
int main (void) {
int i;
struct node *newnode;
// Create list (using actually the same insert-before-first
// that is used in reverse function.
for (i = 0; i < 5; i++) {
newnode = malloc (sizeof (struct node));
newnode->data = i;
newnode->link = first;
first = newnode;
}
// Dump list, reverse it, then dump again.
dumpNodes();
reverse();
dumpNodes();
printf ("==========\n");
return 0;
}
此代码输出:
==========
4
3
2
1
0
==========
0
1
2
3
4
==========
我认为你所追求的是什么。它实际上可以这样做,因为一旦你将 first
加载到遍历列表的指针中,你就可以随意重用 first
。
#include <stddef.h>
typedef struct Node {
struct Node *next;
int data;
} Node;
Node * reverse(Node *cur) {
Node *prev = NULL;
while (cur) {
Node *temp = cur;
cur = cur->next; // advance cur
temp->next = prev;
prev = temp; // advance prev
}
return prev;
}
以下是撤销C中单个链接列表的代码。
这里贴在下面:
// reverse.c
#include <stdio.h>
#include <assert.h>
typedef struct node Node;
struct node {
int data;
Node *next;
};
void spec_reverse();
Node *reverse(Node *head);
int main()
{
spec_reverse();
return 0;
}
void print(Node *head) {
while (head) {
printf("[%d]->", head->data);
head = head->next;
}
printf("NULL\n");
}
void spec_reverse() {
// Create a linked list.
// [0]->[1]->[2]->NULL
Node node2 = {2, NULL};
Node node1 = {1, &node2};
Node node0 = {0, &node1};
Node *head = &node0;
print(head);
head = reverse(head);
print(head);
assert(head == &node2);
assert(head->next == &node1);
assert(head->next->next == &node0);
printf("Passed!");
}
// Step 1:
//
// prev head next
// | | |
// v v v
// NULL [0]->[1]->[2]->NULL
//
// Step 2:
//
// prev head next
// | | |
// v v v
// NULL<-[0] [1]->[2]->NULL
//
Node *reverse(Node *head)
{
Node *prev = NULL;
Node *next;
while (head) {
next = head->next;
head->next = prev;
prev = head;
head = next;
}
return prev;
}
是。我相信你可以用同样的方式你这样做可以交换两个数字而不使用第三个。只需将指针强制转换为int / long并执行XOR操作几次。这是制作一个有趣问题的C技巧之一,但没有任何实际价值。
你能降低O(n)复杂度吗?不,不是真的。如果您认为需要相反的顺序,请使用双向链表。
Robert Sedgewick,“ C语言 ”,Addison-Wesley,第3版,1997年,[第3.4节]
如果不是循环列表,则NULL是最后一个链接。
typedef struct node* link;
struct node{
int item;
link next;
};
/* you send the existing list to reverse() and returns the reversed one */
link reverse(link x){
link t, y = x, r = NULL;
while(y != NULL){
t = y->next;
y-> next = r;
r = y;
y = t;
}
return r;
}
只是为了好玩(虽然尾递归优化应该阻止它吃掉所有堆栈):
Node* reverse (Node *root, Node *end) {
Node *next = root->next;
root->next = end;
return (next ? reverse(next, root) : root);
}
root = reverse(root, NULL);
要在不使用临时变量的情况下交换两个变量,
a = a xor b
b = a xor b
a = a xor b
最快的方法是将其写在一行
a = a ^ b ^ (b=a)
类似地,
使用两次掉期
swap(a,b)
swap(b,c)
使用xor的解决方案
a = a^b^c
b = a^b^c
c = a^b^c
a = a^b^c
一行解决方案
c = a ^ b ^ c ^ (a=b) ^ (b=c)
b = a ^ b ^ c ^ (c=a) ^ (a=b)
a = a ^ b ^ c ^ (b=c) ^ (c=a)
使用相同的逻辑来反转链表。
typedef struct List
{
int info;
struct List *next;
}List;
List* reverseList(List *head)
{
p=head;
q=p->next;
p->next=NULL;
while(q)
{
q = (List*) ((int)p ^ (int)q ^ (int)q->next ^ (int)(q->next=p) ^ (int)(p=q));
}
head = p;
return head;
}
您需要一个跟踪指针,它将跟踪列表。
你需要两个指点:
第一个指针来选择第一个节点。 第二个指针来选择第二个节点。
处理:
移动曲目指针
将第二个节点指向第一个节点
通过将第二个指针指向一个
,将第一个指针移动一步将第二个指针移动一步,将轨迹指针指定给第二个
Node* reverselist( )
{
Node *first = NULL; // To keep first node
Node *second = head; // To keep second node
Node *track = head; // Track the list
while(track!=NULL)
{
track = track->next; // track point to next node;
second->next = first; // second node point to first
first = second; // move first node to next
second = track; // move second node to next
}
track = first;
return track;
}
更具可读性:
Node *pop (Node **root)
{
Node *popped = *root;
if (*root) {
*root = (*root)->next;
}
return (popped);
}
void push (Node **root, Node *new_node)
{
new_node->next = *root;
*root = new_node;
}
Node *reverse (Node *root)
{
Node *new_root = NULL;
Node *next;
while ((next = pop(&root))) {
push (&new_root, next);
}
return (new_root);
}
这是Java中的一个更简单的版本。它只使用两个指针 curr
&amp; <代码>分组代码>
public void reverse(Node head) {
Node curr = head, prev = null;
while (head.next != null) {
head = head.next; // move the head to next node
curr.next = prev; //break the link to the next node and assign it to previous
prev = curr; // we are done with previous, move it to next node
curr = head; // current moves along with head
}
head.next = prev; //for last node
}
我不明白为什么需要返回头部,因为我们将它作为参数传递。我们正在通过链接列表的头部,然后我们也可以更新。以下是简单的解决方案
#include<stdio.h>
#include<conio.h>
struct NODE
{
struct NODE *next;
int value;
};
typedef struct NODE node;
void reverse(node **head);
void add_end(node **head,int val);
void alloc(node **p);
void print_all(node *head);
void main()
{
node *head;
clrscr();
head = NULL;
add_end( &head, 1 );
add_end( &head, 2 );
add_end( &head, 3 );
print_all( head );
reverse( &head );
print_all( head );
getch();
}
void alloc(node **p)
{
node *temp;
temp = (node *) malloc( sizeof(node *) );
temp->next = NULL;
*p = temp;
}
void add_end(node **head,int val)
{
node *temp,*new_node;
alloc(&new_node);
new_node->value = val;
if( *head == NULL )
{
*head = new_node;
return;
}
for(temp = *head;temp->next!=NULL;temp=temp->next);
temp->next = new_node;
}
void print_all(node *head)
{
node *temp;
int index=0;
printf ("\n\n");
if (head == NULL)
{
printf (" List is Empty \n");
return;
}
for (temp=head; temp != NULL; temp=temp->next,index++)
printf (" %d ==> %d \n",index,temp->value);
}
void reverse(node **head)
{
node *next,*new_head;
new_head=NULL;
while(*head != NULL)
{
next = (*head)->next;
(*head)->next = new_head;
new_head = (*head);
(*head) = next;
}
(*head)=new_head;
}
#include <stdio.h>
#include <malloc.h>
tydef struct node
{
int info;
struct node *link;
} *start;
void main()
{
rev();
}
void rev()
{
struct node *p = start, *q = NULL, *r;
while (p != NULL)
{
r = q;
q = p;
p = p->link;
q->link = r;
}
start = q;
}
计算出你现在使用的算法的时间复杂度,很明显它无法改进。
不,没有比现在的O(n)更快的速度。你需要改变每个节点,所以时间与元素的数量成正比,那就是你已经拥有的O(n)。
使用两个指针同时保持O(n)的时间复杂度,可以实现的最快速度,可能只能通过指针的数字转换和交换它们的值来实现。这是一个实现:
#include <stdio.h>
typedef struct node
{
int num;
struct node* next;
}node;
void reverse(node* head)
{
node* ptr;
if(!head || !head->next || !head->next->next) return;
ptr = head->next->next;
head->next->next = NULL;
while(ptr)
{
/* Swap head->next and ptr. */
head->next = (unsigned)(ptr =\
(unsigned)ptr ^ (unsigned)(head->next =\
(unsigned)head->next ^ (unsigned)ptr)) ^ (unsigned)head->next;
/* Swap head->next->next and ptr. */
head->next->next = (unsigned)(ptr =\
(unsigned)ptr ^ (unsigned)(head->next->next =\
(unsigned)head->next->next ^ (unsigned)ptr)) ^ (unsigned)head->next->next;
}
}
void add_end(node* ptr, int n)
{
while(ptr->next) ptr = ptr->next;
ptr->next = malloc(sizeof(node));
ptr->next->num = n;
ptr->next->next = NULL;
}
void print(node* ptr)
{
while(ptr = ptr->next) printf("%d ", ptr->num);
putchar('\n');
}
void erase(node* ptr)
{
node *end;
while(ptr->next)
{
if(ptr->next->next) ptr = ptr->next;
else
{
end = ptr->next;
ptr->next = NULL;
free(end);
}
}
}
void main()
{
int i, n = 5;
node* dummy_head;
dummy_head->next = NULL;
for(i = 1; i <= n ; ++i) add_end(dummy_head, i);
print(dummy_head);
reverse(dummy_head);
print(dummy_head);
erase(dummy_head);
}
我的方法略有不同。我想利用现有的函数(如insert_at(index),delete_from(index))来反转列表(类似于右移操作)。复杂性仍然是O(n),但优点是更多的重用代码。看看another_reverse()方法,让我知道你们都在想什么。
#include <stdio.h>
#include <stdlib.h>
struct node {
int data;
struct node* next;
};
struct node* head = NULL;
void printList(char* msg) {
struct node* current = head;
printf("\n%s\n", msg);
while (current != NULL) {
printf("%d ", current->data);
current = current->next;
}
}
void insert_beginning(int data) {
struct node* newNode = (struct node*) malloc(sizeof(struct node));
newNode->data = data;
newNode->next = NULL;
if (head == NULL)
{
head = newNode;
} else {
newNode->next = head;
head = newNode;
}
}
void insert_at(int data, int location) {
struct node* newNode = (struct node*) malloc(sizeof(struct node));
newNode->data = data;
newNode->next = NULL;
if (head == NULL)
{
head = newNode;
}
else {
struct node* currentNode = head;
int index = 0;
while (currentNode != NULL && index < (location - 1)) {
currentNode = currentNode->next;
index++;
}
if (currentNode != NULL)
{
if (location == 0) {
newNode->next = currentNode;
head = newNode;
} else {
newNode->next = currentNode->next;
currentNode->next = newNode;
}
}
}
}
int delete_from(int location) {
int retValue = -1;
if (location < 0 || head == NULL)
{
printf("\nList is empty or invalid index");
return -1;
} else {
struct node* currentNode = head;
int index = 0;
while (currentNode != NULL && index < (location - 1)) {
currentNode = currentNode->next;
index++;
}
if (currentNode != NULL)
{
// we've reached the node just one prior to the one we want to delete
if (location == 0) {
if (currentNode->next == NULL)
{
// this is the only node in the list
retValue = currentNode->data;
free(currentNode);
head = NULL;
} else {
// the next node should take its place
struct node* nextNode = currentNode->next;
head = nextNode;
retValue = currentNode->data;
free(currentNode);
}
} // if (location == 0)
else {
// the next node should take its place
struct node* nextNode = currentNode->next;
currentNode->next = nextNode->next;
if (nextNode != NULL
) {
retValue = nextNode->data;
free(nextNode);
}
}
} else {
printf("\nInvalid index");
return -1;
}
}
return retValue;
}
void another_reverse() {
if (head == NULL)
{
printf("\nList is empty\n");
return;
} else {
// get the tail pointer
struct node* tailNode = head;
int index = 0, counter = 0;
while (tailNode->next != NULL) {
tailNode = tailNode->next;
index++;
}
// now tailNode points to the last node
while (counter != index) {
int data = delete_from(index);
insert_at(data, counter);
counter++;
}
}
}
int main(int argc, char** argv) {
insert_beginning(4);
insert_beginning(3);
insert_beginning(2);
insert_beginning(1);
insert_beginning(0);
/* insert_at(5, 0);
insert_at(4, 1);
insert_at(3, 2);
insert_at(1, 1);*/
printList("Original List\0");
//reverse_list();
another_reverse();
printList("Reversed List\0");
/* delete_from(2);
delete_from(2);*/
//printList();
return 0;
}
using 2-pointers....bit large but simple and efficient
void reverse()
{
int n=0;
node *temp,*temp1;
temp=strptr;
while(temp->next!=NULL)
{
n++; //counting no. of nodes
temp=temp->next;
}
// we will exchange ist by last.....2nd by 2nd last so.on....
int i=n/2;
temp=strptr;
for(int j=1;j<=(n-i+1);j++)
temp=temp->next;
// i started exchanging from in between ....so we do no have to traverse list so far //again and again for exchanging
while(i>0)
{
temp1=strptr;
for(int j=1;j<=i;j++)//this loop for traversing nodes before n/2
temp1=temp1->next;
int t;
t=temp1->info;
temp1->info=temp->info;
temp->info=t;
i--;
temp=temp->next;
//at the end after exchanging say 2 and 4 in a 5 node list....temp will be at 5 and we will traverse temp1 to ist node and exchange ....
}
}
#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
struct node
{
int data;
struct node *link;
};
struct node *first=NULL,*last=NULL,*next,*pre,*cur,*temp;
void create()
{
cur=(struct node*) malloc(sizeof(struct node));
printf("enter first data to insert");
scanf("%d",&cur->data);
first=last=cur;
first->link=NULL;
}
void insert()
{
int pos,c;
cur=(struct node*) malloc(sizeof(struct node));
printf("enter data to insert and also its position");
scanf("%d%d",&cur->data,&pos);
if(pos==1)
{
cur->link=first;
first=cur;
}
else
{
c=1;
next=first;
while(c<pos)
{
pre=next;
next=next->link;
c++;
}
if(pre==NULL)
{
printf("Invalid position");
}
else
{
cur->link=pre->link;
pre->link=cur;
}
}
}
void display()
{
cur=first;
while(cur!=NULL)
{
printf("data= %d\t address= %u\n",cur->data,cur);
cur=cur->link;
}
printf("\n");
}
void rev()
{
pre=NULL;
cur=first;
while(cur!=NULL)
{
next=cur->link;
cur->link=pre;
pre=cur;
cur=next;
}
first=pre;
}
void main()
{
int choice;
clrscr();
do
{
printf("Options are: -\n1:Create\n2:Insert\n3:Display\n4:Reverse\n0:Exit\n");
printf("Enter your choice: - ");
scanf("%d",&choice);
switch(choice)
{
case 1:
create();
break;
case 2:
insert();
break;
case 3:
display();
break;
case 4:
rev();
break;
case 0:
exit(0);
default:
printf("wrong choice");
}
}
while(1);
}
是的,有一种方法只使用两个指针。即通过创建新的链表,其中第一个节点是给定列表的第一个节点,第一个列表的第二个节点是在新列表的开头添加的,依此类推。
这是我的版本:
void reverse(ListElem *&head)
{
ListElem* temp;
ListElem* elem = head->next();
ListElem* prev = head;
head->next(0);
while(temp = elem->next())
{
elem->next(prev);
prev = elem;
elem = temp;
}
elem->next(prev);
head = elem;
}
,其中
class ListElem{
public:
ListElem(int val): _val(val){}
ListElem *next() const { return _next; }
void next(ListElem *elem) { _next = elem; }
void val(int val){ _val = val; }
int val() const { return _val;}
private:
ListElem *_next;
int _val;
};
我正在使用java来实现这一点,并且方法是测试驱动开发,因此也附加了测试用例。 结果
表示单个节点的Node类 -
package com.adnan.linkedlist;
/**
* User : Adnan
* Email : sendtoadnan@gmail.com
* Date : 9/21/13
* Time : 12:02 PM
*/
public class Node {
public Node(int value, Node node){
this.value = value;
this.node = node;
}
private int value;
private Node node;
public int getValue() {
return value;
}
public Node getNode() {
return node;
}
public void setNode(Node node){
this.node = node;
}
}
将起始节点作为输入并在不使用额外空间的情况下保留它的服务类。
package com.adnan.linkedlist;
/**
* User : Adnan
* Email : sendtoadnan@gmail.com
* Date : 9/21/13
* Time : 11:54 AM
*/
public class SinglyLinkedListReversal {
private static final SinglyLinkedListReversal service
= new SinglyLinkedListReversal();
public static SinglyLinkedListReversal getService(){
return service;
}
public Node reverse(Node start){
if (hasOnlyNodeInLinkedList(start)){
return start;
}
Node firstNode, secondNode, thirdNode;
firstNode = start;
secondNode = firstNode.getNode();
while (secondNode != null ){
thirdNode = secondNode.getNode();
secondNode.setNode(firstNode);
firstNode = secondNode;
secondNode = thirdNode;
}
start.setNode(null);
return firstNode;
}
private boolean hasOnlyNodeInLinkedList(Node start) {
return start.getNode() == null;
}
}
以及涵盖上述场景的测试用例。请注意,您需要junit罐子。我正在使用testng.jar;你可以用任何你喜欢的东西..
package com.adnan.linkedlist;
import org.testng.annotations.Test;
import static org.testng.AssertJUnit.assertTrue;
/**
* User : Adnan
* Email : sendtoadnan@gmail.com
* Date : 9/21/13
* Time : 12:11 PM
*/
public class SinglyLinkedListReversalTest {
private SinglyLinkedListReversal reversalService =
SinglyLinkedListReversal.getService();
@Test
public void test_reverseSingleElement() throws Exception {
Node node = new Node(1, null);
reversalService.reverse(node);
assertTrue(node.getNode() == null);
assertTrue(node.getValue() == 1);
}
//original - Node1(1) -> Node2(2) -> Node3(3)
//reverse - Node3(3) -> Node2(2) -> Node1(1)
@Test
public void test_reverseThreeElement() throws Exception {
Node node3 = new Node(3, null);
Node node2 = new Node(2, node3);
Node start = new Node(1, node2);
start = reversalService.reverse(start);
Node test = start;
for (int i = 3; i >=1 ; i -- ){
assertTrue(test.getValue() == i);
test = test.getNode();
}
}
@Test
public void test_reverseFourElement() throws Exception {
Node node4 = new Node(4, null);
Node node3 = new Node(3, node4);
Node node2 = new Node(2, node3);
Node start = new Node(1, node2);
start = reversalService.reverse(start);
Node test = start;
for (int i = 4; i >=1 ; i -- ){
assertTrue(test.getValue() == i);
test = test.getNode();
}
}
@Test
public void test_reverse10Element() throws Exception {
Node node10 = new Node(10, null);
Node node9 = new Node(9, node10);
Node node8 = new Node(8, node9);
Node node7 = new Node(7, node8);
Node node6 = new Node(6, node7);
Node node5 = new Node(5, node6);
Node node4 = new Node(4, node5);
Node node3 = new Node(3, node4);
Node node2 = new Node(2, node3);
Node start = new Node(1, node2);
start = reversalService.reverse(start);
Node test = start;
for (int i = 10; i >=1 ; i -- ){
assertTrue(test.getValue() == i);
test = test.getNode();
}
}
@Test
public void test_reverseTwoElement() throws Exception {
Node node2 = new Node(2, null);
Node start = new Node(1, node2);
start = reversalService.reverse(start);
Node test = start;
for (int i = 2; i >=1 ; i -- ){
assertTrue(test.getValue() == i);
test = test.getNode();
}
}
}
如果您将链接列表用作堆栈结构,则使用简单的算法:
#include <stdio.h>
#include <stdlib.h>
typedef struct list {
int key;
char value;
struct list* next;
} list;
void print(list*);
void add(list**, int, char);
void reverse(list**);
void deleteList(list*);
int main(void) {
list* head = NULL;
int i=0;
while ( i++ < 26 ) add(&head, i, i+'a');
printf("Before reverse: \n");
print(head);
printf("After reverse: \n");
reverse(&head);
print(head);
deleteList(head);
}
void deleteList(list* l) {
list* t = l;
while ( t != NULL ) {
list* tmp = t;
t = t->next;
free(tmp);
}
}
void print(list* l) {
list* t = l;
while ( t != NULL) {
printf("%d:%c\n", t->key, t->value);
t = t->next;
}
}
void reverse(list** head) {
list* tmp = *head;
list* reversed = NULL;
while ( tmp != NULL ) {
add(&reversed, tmp->key, tmp->value);
tmp = tmp->next;
}
deleteList(*head);
*head = reversed;
}
void add(list** head, int k, char v) {
list* t = calloc(1, sizeof(list));
t->key = k; t->value = v;
t->next = *head;
*head = t;
}
由于对add和malloc的附加函数调用,性能可能会受到影响,因此地址交换的算法更好,但实际创建新列表,因此如果添加回调函数,可以使用其他选项,如排序或删除项目参数反向。
这是C ++ 11中稍微不同但又简单的方法:
#include <iostream>
struct Node{
Node(): next(NULL){}
Node *next;
std::string data;
};
void printlist(Node* l){
while(l){
std::cout<<l->data<<std::endl;
l = l->next;
}
std::cout<<"----"<<std::endl;
}
void reverse(Node*& l)
{
Node* prev = NULL;
while(l){
auto next = l->next;
l->next = prev;
prev=l;
l=next;
}
l = prev;
}
int main() {
Node s,t,u,v;
s.data = "1";
t.data = "2";
u.data = "3";
v.data = "4";
s.next = &t;
t.next = &u;
u.next = &v;
Node* ptr = &s;
printlist(ptr);
reverse(ptr);
printlist(ptr);
return 0;
}
输出此处
以下是使用2个指针(head和r)的一个实现
ListNode * reverse(ListNode* head) {
ListNode *r = NULL;
if(head) {
r = head->next;
head->next = NULL;
}
while(r) {
head = reinterpret_cast<ListNode*>(size_t(head) ^ size_t(r->next));
r->next = reinterpret_cast<ListNode*>(size_t(r->next) ^ size_t(head));
head = reinterpret_cast<ListNode*>(size_t(head) ^ size_t(r->next));
head = reinterpret_cast<ListNode*>(size_t(head) ^ size_t(r));
r = reinterpret_cast<ListNode*>(size_t(r) ^ size_t(head));
head = reinterpret_cast<ListNode*>(size_t(head) ^ size_t(r));
}
return head;
}
这是一个简单的解决方案...
void reverse()
{
node * pointer1 = head->next;
if(pointer1 != NULL)
{
node *pointer2 = pointer1->next;
pointer1->next = head;
head->next = NULL;
head = pointer1;
if(pointer2 != NULL)
{
while(pointer2 != NULL)
{
pointer1 = pointer2;
pointer2 = pointer2->next;
pointer1->next = head;
head = pointer1;
}
pointer1->next = head;
head = pointer1;
}
}
}
只有一个额外的指针可以解决这个问题,对于反向函数必须是静态的。这是O(n)复杂性。
#include<stdio.h>
#include<stdlib.h>
typedef struct List* List;
struct List {
int val;
List next;
};
List reverse(List list) { /* with recursion and one static variable*/
static List tail;
if(!list || !list->next) {
tail = list;
return tail;
} else {
reverse1(list->next);
list->next->next = list;
list->next = NULL;
return tail;
}
}
作为替代方案,您可以使用递归 -
struct node* reverseList(struct node *head)
{
if(head == NULL) return NULL;
if(head->next == NULL) return head;
struct node* second = head->next;
head->next = NULL;
struct node* remaining = reverseList(second);
second->next = head;
return remaining;
}
curr = head;
prev = NULL;
while (curr != NULL) {
next = curr->next; // store current's next, since it will be overwritten
curr->next = prev;
prev = curr;
curr = next;
}
head = prev; // update head
class Node {
Node next;
int data;
Node(int item) {
data = item;
next = null;
}
}
public class LinkedList {
static Node head;
//Print LinkedList
public static void printList(Node node){
while(node!=null){
System.out.print(node.data+" ");
node = node.next;
}
System.out.println();
}
//Reverse the LinkedList Utility
public static Node reverse(Node node){
Node new_node = null;
while(node!=null){
Node next = node.next;
node.next = new_node;
new_node = node;
node = next;
}
return new_node;
}
public static void main(String[] args) {
//Creating LinkedList
LinkedList.head = new Node(1);
LinkedList.head.next = new Node(2);
LinkedList.head.next.next = new Node(3);
LinkedList.head.next.next.next = new Node(4);
LinkedList.printList(LinkedList.head);
Node node = LinkedList.reverse(LinkedList.head);
LinkedList.printList(node);
}
}