链表分为单链表,双向链表和循环链表,是一种链式存储结构,由一个个结点链式构成,结点包含数据域和指针域,其中单链表是只有一个指向后驱结点的指针,双向链表除头结点和尾结点外,每个结点都有一个前驱指针和一个后继指针,循环链表的尾结点的指针指向头结点.
相比数组而言,链表的插入和删除比较快,查询慢.
本文主要以单链表为例,介绍下链表的常用算法操作.
单链表的结构:
在java语言中,链表的每个结点用Node类来表示:
package com.linkedlist;
public class Node {
private int data;// 结点数据
private Node next;// 下一个结点
public Node(int data) {
this.data = data;
}
public int getData() {
return data;
}
public void setData(int data) {
this.data = data;
}
public Node getNext() {
return next;
}
public void setNext(Node next) {
this.next = next;
}
}
定义一个链表操作类,里面包含常用的操作:
package com.linkedlist;
import java.util.Hashtable;
public class LinkedListOperator {
private Node head = null;// 头结点
// 在链表的末尾增加一个结点
private void addNode(int data) {
Node newNode = new Node(data);
if (head == null) {
head = newNode;
return;
}
Node temp = head;
while (temp.getNext() != null) {
temp = temp.getNext();
}
temp.setNext(newNode);
}
// 打印链表结点
private void printLink() {
Node curNode = head;
while (curNode != null) {
System.out.println(curNode.getData());
curNode = curNode.getNext();
}
System.out.println("===========");
}
// 求链表长度
private int getLength() {
int len = 0;
Node curNode = head;
while (curNode != null) {
len++;
curNode = curNode.getNext();
}
return len;
}
// 删除某一个结点
private boolean delNode(int index) {
if (index < 1) {
return false;
}
if (index == 1) {
head = head.getNext();
return true;
}
Node preNode = head;
Node curNode = head.getNext();
int n = 1;
while (curNode.getNext() != null) {
if (n == index) {
preNode.setData(curNode.getData());
preNode.setNext(curNode.getNext());
return true;
}
preNode = preNode.getNext();
curNode = curNode.getNext();
n++;
}
if (curNode.getNext() == null) {
preNode.setNext(null);
}
return false;
}
// 链表排序:选择排序法,从小到大
private void sortList() {
Node curNode = head;
while (curNode != null) {
Node nextNode = curNode.getNext();
while (nextNode != null) {
if (curNode.getData() > nextNode.getData()) {
int temp = curNode.getData();
curNode.setData(nextNode.getData());
nextNode.setData(temp);
}
nextNode = nextNode.getNext();
}
curNode = curNode.getNext();
}
}
// 去掉重复元素
private void distinctLink() {
Hashtable<Integer, Integer> map = new Hashtable<Integer, Integer>();
Node curNode = head;
Node preNode = null;
while (curNode != null) {
if (map.containsKey(curNode.getData())) {
preNode.setData(curNode.getData());
preNode.setNext(curNode.getNext());
} else {
map.put(curNode.getData(), 1);
preNode = curNode;
}
curNode = curNode.getNext();
}
}
// 返回倒数第k个结点,定义两个指针,第一个指针向前移动K-1次,之后两个指针同时前进,
// 当第一个指针到达末尾时,第二个指针所在的位置即为倒数第k个结点
private Node getReverNode(int k) {
if (k < 1) {
return null;
}
Node first = head;
Node second = head;
for (int i = 0; i < k - 1; i++) {
first = first.getNext();
}
while (first.getNext() != null) {
first = first.getNext();
second = second.getNext();
}
return second;
}
// 反转链表
private void reserveLink() {
Node preNode = null;
Node curNode = head;
Node tempNode = null;
while (curNode != null) {
tempNode = curNode.getNext();
curNode.setNext(preNode);
preNode = curNode;
curNode = tempNode;
}
head = preNode;
}
// 寻找链表的中间结点
private Node getMiddleNode() {
Node slowNode = head;
Node quickNode = head;
while (slowNode.getNext() != null && quickNode.getNext() != null) {
slowNode = slowNode.getNext();
quickNode = quickNode.getNext().getNext();
}
return slowNode;
}
// 判断链表是否有环
private boolean isRinged() {
if (head == null) {
return false;
}
Node slowNode = head;
Node quickNode = head;
while (slowNode.getNext() != null && quickNode.getNext() != null) {
slowNode = slowNode.getNext();
quickNode = quickNode.getNext().getNext();
if (slowNode.getData() == quickNode.getData()) {
return true;
}
}
return false;
}
// 删除指定结点
private boolean delNode(Node node) {
if (node.getNext() == null) {
return false;// 在不知道头结点的情况下,没法删除单链表的尾结点
}
node.setData(node.getNext().getData());
node.setNext(node.getNext().getNext());
return true;
}
// 判断两个链表是否相交:相交的链表的尾结点相同
private boolean isCross(Node n1, Node n2) {
while (n1.getNext() != null) {
n1 = n1.getNext();
}
while (n2.getNext() != null) {
n2 = n2.getNext();
}
if (n1.getData() == n2.getData()) {
return true;
}
return false;
}
// 求相交链表的起始点
private Node getFirstCrossNode(LinkedListOperator l1, LinkedListOperator l2) {
int len = l1.getLength() - l2.getLength();
Node n1 = l1.head;
Node n2 = l2.head;
if (len > 0) {
for (int i = 0; i < len; i++) {
n1 = n1.getNext();
}
} else {
for (int i = 0; i < len; i++) {
n2 = n2.getNext();
}
}
while (n1.getData() != n2.getData()) {
n1 = n1.getNext();
n2 = n2.getNext();
}
return n1;
}
public static void main(String[] args) {
LinkedListOperator llo = new LinkedListOperator();
llo.addNode(10);
llo.addNode(4);
llo.addNode(6);
llo.addNode(8);
llo.printLink();
// llo.delNode(4);
// llo.sortList();
// llo.distinctLink();
// System.out.println(llo.getReverNode(3).getData());
// llo.reserveLink();
// System.out.println(llo.getMiddleNode().getData());
// System.out.println(llo.isRinged());
llo.delNode(llo.head.getNext().getNext());
llo.printLink();
}
}