生成随机加减法题目

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import java.util.Random;   public class Main {     public static void main(String[] args) {         Random rand = new Random();           for (int i = 0; i < 20; i++) {             int num1 = rand.nextInt(100) + 1;             int num2 = rand.nextInt(100) + 1;             int operator = rand.nextInt(2); // 0代表加号，1代表减号             char operatorChar = operator == 0 ? '+' : '-';               System.out.println(num1 + " " + operatorChar + " " + num2 + " = ");         }     } }

　　改进目标：

1. 避免重复题目
2. 可控制题目数量
3. 增加乘除法