第1关 

两整数的四则运算

package step1;

import java.util.Scanner;

public class Arithmetic2Num {
    public static void main(String[] args) {
// ---------------------Begin------------------------
         Scanner sc=new Scanner(System.in);
         int a=sc.nextInt();
         int b=sc.nextInt();
          System.out.print("a+b=");
           System.out.println(a+b);
                       System.out.print("a*b=");
           System.out.println(a*b);
            System.out.print("a-b=");
           System.out.println(a-b);

            System.out.print("a/b=");
           System.out.println(a/b);

// ---------------------End------------------------
    }
}

第2关 打印三角形

package step2;

import java.util.Scanner;

public class PosTriangle {
   public static  void prin(int n,int n2)
        {
            int num=n*2-1;
            if(n==1){
                for(int i=0;i<n2;i++)System.out.print(' ');
                System.out.println('*');
                return;
            }
            prin(n-1,n2+1);
            for(int i=0;i<n2;i++)System.out.print(' ');
            for(int i=0;i<num;i++)System.out.print('*');
            System.out.println();

        }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        //定义输入的行数:
        int n = scanner.nextInt();
        // ---------------------Begin------------------------          
          prin(n,0);

        // ---------------------End------------------------
    }
}

第3关 循环之倒三角形

package step3;

import java.util.Scanner;

public class NegTriangle {
    public static  void prin(int n,int x)
        {
            int num=n*2-1;
            if(n==x){
                for(int i=0;i<num;i++)System.out.print('*');
                System.out.println();
                return;
            }
            prin(n+1,x);
            for(int i=0;i<x-n;i++)System.out.print(' ');
            for(int i=0;i<num;i++)System.out.print('*');
            System.out.println();

        }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        //定义输入的行数:
        int n = scanner.nextInt();
        // ---------------------Begin------------------------
        prin(1,n);

    
        // ---------------------End------------------------

    }
}

第4关 水仙花数

package step4;

import java.util.Scanner;

public class narcissisticNumber {
   public static boolean dfs(int x){
        int sum=0;
        int num=x;
        while(num!=0){
            int m=num%10;
            sum=sum+(m*m*m);
            if(sum>x)return false;      
            num=num/10;
        }
        if(sum==x) return true;
        else return false;
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        //获取起始范围
        int i = scanner.nextInt();
        //获取终止范围
        int j = scanner.nextInt();
        // ---------------------Begin------------------------
        int l=0;
        for(int k=i;k<=j;k++)
        { 
            if(dfs(k))
            System.out.println(k);
            else l++;
         }
            if(l==(j-i+1)){
            System.out.print(i);
            System.out.print('~');
            System.out.print(j);
            System.out.println("范围内无水仙花数！");
            }
        // ---------------------End------------------------
    }
}

第5关 a与b之间的素数

package step5;

import java.util.Scanner;

public class PrimeNumber {
    public static boolean find(int x){
        if(x==1)return false;
        for(int i=2;i<=9;i++){
            if(x%i==0&&i<x)return false;
        }
        return true;
    }
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        // ---------------------Begin------------------------
               
        int i = scan.nextInt();
 
        int j = scan.nextInt();
        System.out.print(i);
        System.out.print("到");
        System.out.print(j);
        System.out.println("之间的素数有：");
        for(int k=i;k<=j;k++){
               if(find(k)){ 
                   System.out.print(k);
                   System.out.print(' ');
                   }
        }
    
    }

        // ---------------------End------------------------

}

第6关 

余X的整数

package step6;

import java.util.Scanner;

public class LeftXnumber {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        // ---------------------Begin------------------------
        int a=scanner.nextInt();
        int b=scanner.nextInt();
        int c=scanner.nextInt();
        for(int i=a;i<=b;i++){
             if(i%c==0)System.out.println(i);
        }
       
       
        // ---------------------End------------------------
    }
}

第7关 求解1元2次方程

package step7;

import java.util.Scanner;

public class SolveEquations {
    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);
       double a=scanner.nextDouble();
         double b=scanner.nextDouble();
          double c=scanner.nextDouble();
        double delta=b*b-4*a*c;
        if(delta>0){
            double x1=(-b+Math.sqrt(delta))/(2*a);
            double x2=(-b-Math.sqrt(delta))/(2*a);
            System.out.printf("方程有两个解：x1=%.2f x2=%.2f",x1,x2);
        }else if(delta==0){
            double x=-b/(2*a);
            System.out.printf("方程有一个解：x1=x2=&.2f",x);
        }else {
            System.out.println("此方程无解");
        }
        // ---------------------End------------------------

        
        // ---------------------End------------------------

    }
}