面试笔试题

1.使用递归算法,求1+2+3..100=?

    public static int jisuan(int x) {
        System.out.println("x = " + x);
        if (x == 1) {
            return 1;
        } else {
            return x + jisuan(x - 1);
        }
    }

2.使用递归算法,第一个人10,第二个比第一个大2,求第八个人?

public static int computeAge(int n) {
        if (n == 1) {
            return 10;
        } else {
            return computeAge(n - 1) + 2;
        }
    }

3.有ab两个文件,a 以换行符分割,b以换行或者空格分割,把ab两个文件交替合并到c文件中去.

public static void main(String[] args) throws Exception {
        File file_a = new File("E:\\idea\\guanchazhe\\src\\file\\a.txt");
        File file_b = new File("E:\\idea\\guanchazhe\\src\\file\\b.txt");

        InputStreamReader isr_a = new InputStreamReader(new FileInputStream(file_a), "UTF-8");
        BufferedReader read_a = new BufferedReader(isr_a);


        InputStreamReader isr_b = new InputStreamReader(new FileInputStream(file_b), "UTF-8");
        BufferedReader read_b = new BufferedReader(isr_b);

        List<String> list_a = new ArrayList<>();
        List<String> list_b_temp = new ArrayList<>();
        List<String> list_b = new ArrayList<>();
        List<String> list_c = new ArrayList<>();
        String line;
        while ((line = read_a.readLine()) != null) {
            list_a.add(line);
        }

        while ((line = read_b.readLine()) != null) {
            list_b_temp.add(line);
        }

        for (String str : list_b_temp) {
            String[] split = str.split(" ");
            for (String str_sp : split) {
                list_b.add(str_sp);
            }
        }
        int size_a = list_a.size();
        int size_b = list_b.size();
        for (int i = 0; i < (size_a > size_b ? size_a : size_b); i++) {
            if (i < size_a) {
                list_c.add(list_a.get(i));
            }
            if (i < size_b) {
                list_c.add(list_b.get(i));
            }
        }

        BufferedWriter out_c = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("E:\\idea\\guanchazhe\\src\\file\\c.txt", true)));
        for (String str : list_c) {
            out_c.write(str);
            out_c.newLine();
        }
        out_c.flush();
        read_a.close();
        out_c.close();
    }

图书馆有AB两个在线在职,user1,user2订阅A,user3,user4,user1订阅B,使用订阅发布模式使AB在跟新时候,通知1234.

public interface ILibrary {

    void addObservers(IObserver observers ,String type);//添加观察者

    void deleteObservers(IObserver observers,String type);//删除观察者

    void notifyAllObservers(String msg,String type);//通知所有的观察者
}


public interface IObserver {

    void update(String msg);
}


public class Library implements ILibrary {
    private List<IObserver> listA = new ArrayList<>();
    private List<IObserver> listB = new ArrayList<>();

    @Override
    public void addObservers(IObserver observers, String type) {
        if ("A".equals(type)) {
            listA.add(observers);
        } else if ("B".equals(type)) {
            listB.add(observers);
        } else {

        }
    }

    @Override
    public void deleteObservers(IObserver observers, String type) {
        if ("A".equals(type)) {
            listA.remove(observers);
        } else if ("B".equals(type)) {
            listA.remove(observers);
        } else {

        }
    }

    @Override
    public void notifyAllObservers(String msg, String type) {
        if ("A".equals(type)) {
            for (IObserver observer : listA) {
                observer.update(msg);
            }
        } else if ("B".equals(type)) {
            for (IObserver observer : listB) {
                observer.update(msg);
            }
        } else {

        }
    }
}


public class UserA implements IObserver {
    @Override
    public void update(String msg) {
        System.out.println("用户A收到消息:"+msg);
    }
}



public class UserB implements IObserver {
    @Override
    public void update(String msg) {
        System.out.println("用户B收到消息:"+msg);
    }
}

public class UserC implements IObserver {
    @Override
    public void update(String msg) {
        System.out.println("用户C收到消息:"+msg);
    }
}



public class UserD implements IObserver {
    @Override
    public void update(String msg) {
        System.out.println("用户D收到消息:"+msg);
    }
}



public static void main(String[] args) {
        Library library=new Library();

        IObserver userA = new UserA();
        IObserver userB = new UserB();
        IObserver userC = new UserC();
        IObserver userD = new UserD();

        library.addObservers(userA,"A");
        library.addObservers(userB,"A");

        library.addObservers(userC,"B");
        library.addObservers(userD,"B");
        library.addObservers(userA,"B");

        library.notifyAllObservers("我发布了新的杂志A","A");
        library.notifyAllObservers("我发布了新的杂志B","B");



    }