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();  }}