求集合差的几种算法

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([email protected]) * @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([email protected]) * @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([email protected]) * @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([email protected]) * @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([email protected]) * @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([email protected]) * @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()); } } }