数据结构（三）之单链表反向查找

一、反向查找单链表

1、简单查找

　　先遍历获取单链表单长度n，然后通过计算得到倒数第k个元素的下标为n-k，然后查找下标为n-k的元素。

2、优化查找

先找到下标为k的元素为记录点p1，然后设置新的记录点p2的下标从0开始，同时遍历两个记录点，直到p1的值为null，p2是倒数第k个元素。

单链表结点：

package cn.edu.scau.mk;/**** @author MK* @param <T>*/
public class Node<T> {private T data;private Node<T> next = null;public Node(T data) {this.data = data;}public T getData() {return data;}public void setData(T data) {this.data = data;}public Node<T> getNext() {return next;}public void setNext(Node<T> next) {this.next = next;}}

View Code

链表：

package cn.edu.scau.mk;import java.util.Comparator;/**** @author MK* @param <T>*/
public class LinkedList<T> {protected Node<T> head = null;/*** 添加** @param data*/public void add(T data) {//头结点为nullif (head == null) {head = new Node<>(data);return;}//寻找末结点Node<T> curNode = head;while (curNode.getNext() != null) {curNode = curNode.getNext();}curNode.setNext(new Node<>(data));//添加结点
    }/*** 删除** @param index 下标,从0开始* @return*/public boolean delete(int index) {//没有数据if (head == null) {return false;}//删除头结点if (index == 0) {head = head.getNext();}Node<T> curNode = head;int i = 1;while (curNode.getNext() != null) {if (i == index) {curNode.setNext(curNode.getNext().getNext());return true;}i++;curNode = curNode.getNext();}throw new IndexOutOfBoundsException("Index: "+index+", Size: "+i);}/*** 长度** @return*/public int length() {int len = 0;Node<T> curNode = head;while (curNode != null) {len++;curNode = curNode.getNext();}return len;}/*** 查找* @param index 位置* @return */public T get(int index) {Node<T> curNode = head;int i = 0;while (curNode != null) {if (i == index) {return curNode.getData();}i++;curNode = curNode.getNext();}throw new IndexOutOfBoundsException("Index: "+index+", Size: "+i);}/*** 排序* @param comparator 比较器*/public void sort(Comparator<T> comparator) {//没有数据if (head == null) {return;}Node<T> curNode = head;Node<T> nextNode;Node<T> minNode;while (curNode.getNext() != null) {minNode = curNode;  //默认最小结点为当前结点nextNode = curNode.getNext();  //下一个结点while (nextNode != null) {//比当前结点小，记录最小结点if(comparator.compare(curNode.getData(), nextNode.getData())>0){minNode=nextNode;}nextNode=nextNode.getNext();  //继续与下一个结点比较
            }//最小结点不是当前结点，交换数据if(minNode!=curNode){T data=curNode.getData();curNode.setData(minNode.getData());minNode.setData(data);}curNode=curNode.getNext();  //移至下一个结点
        }}/*** 打印输出*/public  void print() {Node<T> curNode = head;while (curNode!=null) {            System.out.print(curNode.getData()+" ");curNode=curNode.getNext();}System.out.println();}
}

View Code

二、简单查找

package cn.edu.scau.mk;import java.util.HashMap;/**** @author MK* @param <T>*/
public class OpLinkedList<T> extends LinkedList<T> {/*** 简单反向查找* @param index 倒数个数，从1开始* @return */public T getByLastIndex(int index) {//倒数个数小于1if (index < 1) {throw new IndexOutOfBoundsException("Last Index : " + index);}int len=this.length();//链表长度//倒数个数越界if (head == null||len<index) {throw new IndexOutOfBoundsException("Last Index: " + index + ", Size: " + 0);}len=len-index;//第n-k个Node<T> curNode = head;  //默认第0个for (int i = 0; i < len; i++) {          curNode = curNode.getNext();//第i+1个
        }return curNode.getData();}}

三、优化查找

package cn.edu.scau.mk;import java.util.HashMap;/**** @author MK* @param <T>*/
public class OpLinkedList<T> extends LinkedList<T> {/***优化反向查找* @param index 倒数个数，从1开始* @return*/public T getByLastIndex(int index) {if (index < 1) {throw new IndexOutOfBoundsException("Last Index : " + index);}if (head == null) {throw new IndexOutOfBoundsException("Last Index: " + index + ", Size: " + 0);}//查找第index个结点Node<T> curNode = head;for (int i = 0; i < index; i++) {if (curNode==null) {throw new IndexOutOfBoundsException("Last Index: " + index + ", Size: " + i);         }curNode = curNode.getNext();}//循环直到curNode为null，indexNode刚好为倒数index个   Node<T> indexNode = head;while (curNode != null) {            curNode =curNode.getNext();indexNode=indexNode.getNext();}return indexNode.getData();}
}