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
import java.util.ArrayList; import java.util.List; /** * 利用双重循环实现的筛选 */ 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
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 */ 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
import java.util.ArrayList; import java.util.List; /** * 使用工具类的筛选去除 */ 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
import java.util.ArrayList; import java.util.List; /** * 使用二叉樹的筛选去除 */ 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); } } }
当然还有其它的一些算法这次就不列举了。