原题（这里使用了数组代替集合）
有两个数组：
String[] arr01={"Andy","Bill","Cindy","Douglas","Felex","Green"};
String[] arr02={"Andy","Bill","Felex","Green","Gates"};
求存在于arr01而不存在于arr02的元素的集合？
最容易想到的解法-双重循环
package com.junglesong;
import java.util.ArrayList;
import java.util.List;
/** *//**
* 利用双重循环实现的筛选
* @author: sitinspring(junglesong@gmail.com)
* @date: 2008-3-8
*/
public class DoubleCycling
{
public static void main(String[] args){
String[] arr01={"Andy","Bill","Cindy","Douglas","Felex","Green"};
String[] arr02={"Andy","Bill","Felex","Green","Gates"};
// 筛选过程，注意其中异常的用途
List<String> ls=new ArrayList<String>();
for(String str:arr01){
try{
ls.add(getNotExistStr(str,arr02));
}
catch(Exception ex){
continue;
}
}
// 取得结果
Object[] arr03=ls.toArray();
for(Object str:arr03){
System.out.println(str);
}
}
/** *//**
* 查找数组Arr中是否包含str，若包含抛出异常，否则将str返回
* @param str
* @param arr
* @return
* @throws Exception
*/
public static String getNotExistStr(String str,String[] arr) throws Exception{
for(String temp:arr){
if(temp.equals(str)){
throw new Exception("");
}
}
return str;
}
}
速度较高的解法-利用哈希表
package com.junglesong;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Hashtable;
import java.util.List;
import java.util.Map;
/** *//**
* 利用哈希表进行筛选
* @author: sitinspring(junglesong@gmail.com)
* @date: 2008-3-8
*/
public class HashtableFilter{
public static void main(String[] args){
String[] arr01={"Andy","Bill","Cindy","Douglas","Felex","Green"};
String[] arr02={"Andy","Bill","Felex","Green","Gates"};
Map<String,String> ht=new Hashtable<String,String>();
// 將arr02所有元素放入ht
for(String str:arr02){
ht.put(str, str);
}
// 取得在ht中不存在的arr01中的元素
List<String> ls=new ArrayList<String>();
for(String str:arr01){
if(ht.containsKey(str)==false){
ls.add(str);
}
}
// 取得结果
Object[] arr03=ls.toArray();
for(Object str:arr03){
System.out.println(str);
}
}
}
最方便的解法-利用工具类
package com.junglesong;
import java.util.ArrayList;
import java.util.List;
/** *//**
* 使用工具类的筛选去除
* @author: sitinspring(junglesong@gmail.com)
* @date: 2008-3-8
*/
public class Tool{
public static void main(String[] args){
String[] arr01={"Andy","Bill","Cindy","Douglas","Felex","Green"};
String[] arr02={"Andy","Bill","Felex","Green","Gates"};
// 直接转的话，生成的List不支持removeAll
List<String> ls01=new ArrayList<String>();
for(String str:arr01){
ls01.add(str);
}
// 同上
List<String> ls02=new ArrayList<String>();
for(String str:arr02){
ls02.add(str);
}
// 去除arr01中存在于arr02中的元素
ls01.removeAll(ls02);
// 取得结果
Object[] arr03=ls01.toArray();
for(Object str:arr03){
System.out.println(str);
}
}
}
利用二叉树的解法
package com.junglesong.binarytree;
import java.util.ArrayList;
import java.util.List;
/** *//**
* 使用二叉樹的筛选去除
* @author: sitinspring(junglesong@gmail.com)
* @date: 2008-3-8
*/
public class Test{
public static void main(String[] args){
String[] arr01={"Andy","Bill","Cindy","Douglas","Felex","Green"};
String[] arr02={"Andy","Bill","Felex","Green","Gates"};
// 以數組2為基礎創建二叉樹
Tree tree=new Tree();
for(String str:arr02){
tree.insert(str);
}
// 將在二叉樹中不存在的元素放入鏈錶
List<String> ls=new ArrayList<String>();
for(String str:arr01){
if(tree.find(str)==null){
ls.add(str);
}
}
// 輸出
for(String str:ls){
System.out.println(str);
}
}
}
二叉树节点类：
package com.junglesong.binarytree;
/** *//**
* 二叉樹節點類
* @author: sitinspring(junglesong@gmail.com)
* @date: 2008-3-8
*/
public class Node{
private String data;
private Node left;
private Node right;
public Node(String data){
this.data=data;
}
public String getData() {
return data;
}
public Node getLeft() {
return left;
}
public Node getRight() {
return right;
}
public void setData(String data) {
this.data = data;
}
public void setLeft(Node left) {
this.left = left;
}
public void setRight(Node right) {
this.right = right;
}
}
二叉树树类：
package com.junglesong.binarytree;
/** *//**
* 二叉樹類
* @author: sitinspring(junglesong@gmail.com)
* @date: 2008-3-8
*/
public class Tree{
/** *//**
* 根節點
*/
private Node root;
/** *//**
* 插入一個值
* @param str
*/
public void insert(String str){
Node node=new Node(str);
if(root==null){
root=node;
}
else{
Node curr=root;
Node parrent;
while(true){
parrent=curr;
if(str.compareTo(curr.getData())>0){
curr=curr.getRight();
if(curr==null){
parrent.setRight(node);
return;
}
}
else{
curr=curr.getLeft();
if(curr==null){
parrent.setLeft(node);
return;
}
}
}
}
}
/** *//**
* 尋找一個值對應的節點
* @param str
* @return
*/
public Node find(String str){
Node curr=root;
while(curr.getData().equals(str)==false){
if(str.compareTo(curr.getData())>0){
curr=curr.getRight();
}
else{
curr=curr.getLeft();
}
if(curr==null){
return null;
}
}
return curr;
}
/** *//**
* 輸出
*
*/
public void printAll(){
inorder(root);
}
/** *//**
* 中序遍歷
* @param node
*/
private void inorder(Node node){
if(node!=null){
inorder(node.getLeft());
if(node.getData().equals("EqualMark")==false){
System.out.println(node.getData());
}
inorder(node.getRight());
}
}
}
代码下载：
http://www.blogjava.net/Files/junglesong/RemoveAll20080308023355.rar