阿里探花笔试

1.策略模式 实现一个场景，输入两个数字和一个操作类型（加-add，减-subtract，乘-multi，除-devise）,输出计算结果，要求不能使用if-else 或switch等条件控制语句 ，请使用java 实现 并且给出思路

// 1. 定义策略接口
interface CalculatorStrategy {
    double calculate(double num1, double num2);
}

// 2. 实现具体策略类：加法策略
class AdditionStrategy implements CalculatorStrategy {
    @Override
    public double calculate(double num1, double num2) {
        return num1 + num2;
    }
}

// 减法策略
class SubtractionStrategy implements CalculatorStrategy {
    @Override
    public double calculate(double num1, double num2) {
        return num1 - num2;
    }
}

// 乘法策略
class MultiplicationStrategy implements CalculatorStrategy {
    @Override
    public double calculate(double num1, double num2) {
        return num1 * num2;
    }
}

// 除法策略
class DivisionStrategy implements CalculatorStrategy {
    @Override
    public double calculate(double num1, double num2) {
        if (num2 == 0) {
            throw new IllegalArgumentException("除数不能为0");
        }
        return num1 / num2;
    }
}

// 3. 创建上下文类
class CalculatorContext {
    private CalculatorStrategy strategy;

    public void setStrategy(CalculatorStrategy strategy) {
        this.strategy = strategy;
    }

    public double executeStrategy(double num1, double num2) {
        return strategy.calculate(num1, num2);
    }
}

public class Main {
    public static void main(String[] args) {
        // 示例操作数
        double num1 = 10;
        double num2 = 5;
        // 示例操作类型
        String operation = "multi"; 

        CalculatorContext context = new CalculatorContext();
        // 利用Map存储操作类型与对应策略对象的映射关系
        java.util.Map<String, CalculatorStrategy> strategyMap = new java.util.HashMap<>();
        strategyMap.put("add", new AdditionStrategy());
        strategyMap.put("subtract", new SubtractionStrategy());
        strategyMap.put("multi", new MultiplicationStrategy());
        strategyMap.put("devise", new DivisionStrategy());

        CalculatorStrategy selectedStrategy = strategyMap.get(operation);
        if (selectedStrategy!= null) {
            context.setStrategy(selectedStrategy);
            double result = context.executeStrategy(num1, num2);
            System.out.println("计算结果: " + result);
        } else {
            System.out.println("不支持的操作类型");
        }
    }
}

2. 测题目一: A系统提供的login服务，有外部“很多”系统在调用该服务实现其登录逻辑（比如B、C、D等等系统）

现在需要你实现以下逻辑：
1，在A系统上统计各个系统login服务的调用次数 2，把统计出来的每个系统的调用次数做一次升序排序 提示：*/ //登录伪代码如下，各个系统调用本方法登录 // systemName系统名称、userId 用户ID //在本方法中把每个系统调用次数进行统计并用集合存储 public void login(String systemName,String userId) {

}

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class LoginServiceStatistics {
    // 使用HashMap来记录系统名称和对应的调用次数
    private static Map<String, Integer> callCountMap = new HashMap<>();

    public static void login(String systemName, String userId) {
        // 获取当前系统名称对应的调用次数，如果不存在则默认为0，然后加1
        callCountMap.put(systemName, callCountMap.getOrDefault(systemName, 0) + 1);
    }

    public static List<Map.Entry<String, Integer>> getSortedCallCounts() {
        // 将HashMap的Entry集合转换为ArrayList，便于排序
        List<Map.Entry<String, Integer>> entryList = new ArrayList<>(callCountMap.entrySet());

        // 使用自定义比较器按照调用次数进行升序排序
        entryList.sort((e1, e2) -> e1.getValue().compareTo(e2.getValue()));

        return entryList;
    }

    public static void main(String[] args) {
        // 模拟不同系统调用登录服务
        login("B", "user1");
        login("C", "user2");
        login("B", "user3");
        login("D", "user4");
        login("C", "user5");

        List<Map.Entry<String, Integer>> sortedList = getSortedCallCounts();
        for (Map.Entry<String, Integer> entry : sortedList) {
            System.out.println(entry.getKey() + "系统调用次数: " + entry.getValue());
        }
    }
}

3.使用java 三个线程循环打印ABC10次

import java.util.concurrent.Semaphore;

public class PrintABCWithSemaphore {
    // 定义三个信号量，分别控制三个线程的执行顺序
    private static Semaphore semaphoreA = new Semaphore(1);
    private static Semaphore semaphoreB = new Semaphore(0);
    private static Semaphore semaphoreC = new Semaphore(0);

    static class ThreadA implements Runnable {
        @Override
        public void run() {
            try {
                for (int i = 0; i < 10; i++) {
                    semaphoreA.acquire();
                    System.out.print("A");
                    semaphoreB.release();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    static class ThreadB implements Runnable {
        @Override
        public void run() {
            try {
                for (int i = 0; i < 10; i++) {
                    semaphoreB.acquire();
                    System.out.print("B");
                    semaphoreC.release();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    static class ThreadC implements Runnable {
        @Override
        public void run() {
            try {
                for (int i = 0; i < 10; i++) {
                    semaphoreC.acquire();
                    System.out.println("C");
                    semaphoreA.release();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        new Thread(new ThreadA()).start();
        new Thread(new ThreadB()).start();
        new Thread(new ThreadC()).start();
    }
}