第四次编程作业总结

import java.util.Scanner;

class Demo04_01{
    public static int sumDigits(long n) {
        int sum = 0;
        while (n>0) {
            sum = sum + (int)(n % 10);
            n /= 10;
        }
        return sum;
    }

    public static void main(String[] args) {
        System.out.print("请输入一个正整数：");
        Scanner scanner = new Scanner(System.in);
        System.out.println("这个整数所有数字的和为：" + sumDigits(scanner.nextLong()));
    }
}
import java.util.Scanner;

class Demo04_02 {
    public static int reverse(int number) {
        int sum = 0;
        while (number != 0){
            sum = sum * 10 + number % 10;
            number /= 10;
        }
        return sum;
    }

    public static boolean isPalindrome(int number) {
        if (number == reverse(number)) {
            return true;
        }
        else {
            return false;
        }
    }

    public static void main(String[] args) {
        System.out.print("请输入一个整数值：");
        Scanner scanner = new Scanner(System.in);
        if (isPalindrome(scanner.nextInt())) {
            System.out.println("这个整数是回文数.");
        }
        else {
            System.out.println("这个整数不是回文数.");
        }
    }
}
import java.util.Scanner;

class Demo04_03{
    public static void displayPattern(int n) {
        for(int i=1;i<=n;i++){
            for(int k=1;k<=n-i;k++){
                System.out.print("  ");
            }
            for(int j=i;j>=1;j--){
                System.out.print(j+" ");
            }
            System.out.println();
        }
    }

    public static void main(String[] args) {
        System.out.print("请输入打印的行数：");
        Scanner scanner = new Scanner(System.in);
        displayPattern(scanner.nextInt());
    }
}
import java.util.Scanner;

class Demo04_05{
    public static double sqrt(long n) {
        double nextGuess = 0;
        double lastGuess = 1;
        while (true) {
            nextGuess = (lastGuess + n / lastGuess) / 2;
            if(Math.abs(nextGuess - lastGuess) < 0.0001) {
                return nextGuess;
            }
            else {
                double temp;
                temp = nextGuess;
                nextGuess = lastGuess;
                lastGuess = temp;
            }
        }
    }

    public static void main(String[] args) {
        System.out.print("输入一个正整数：");
        Scanner scanner = new Scanner(System.in);
        double n = sqrt(scanner.nextLong());
        System.out.print("这个数的平方根为" + n);
    }
}
import java.util.Scanner;

class Demo04_06 {
    public static int reverse(int number) {
        int sum = 0;
        while (number != 0){
            sum = sum * 10 + number % 10;
            number /= 10;
        }
        return sum;
    }

    public static boolean isPalindrome(int number) {
        if (number == reverse(number)) {
            return true;
        }
        else {
            return false;
        }
    }

    public static boolean isPrimeNumber(int number) {
        boolean flag = true;
        for (int i = 2; i <= number / 2; i++) {
            if (number % i == 0) {
                flag = false;
            }
        }
        return flag;
    }

    public static void main(String[] args) {
        int count = 1;
        for (int i = 2; i <= 1000; i++) {
            if (isPalindrome(i) && isPrimeNumber(i)) {
                System.out.print(i + " ");
                count++;
            }
            if (count % 11 == 0) {
                count = 1;
                System.out.println();
            }
            
        }
        
    }
}
import java.util.Scanner;

class Demo04_07 {
    public static int reverse(int number) {
        int sum = 0;
        while (number != 0){
            sum = sum * 10 + number % 10;
            number /= 10;
        }
        return sum;
    }

    public static boolean isPrimeNumber(int number) {
        boolean flag = true;
        for (int i = 2; i <= number / 2; i++) {
            if (number % i == 0) {
                flag = false;
            }
        }
        return flag;
    }

    public static void main(String[] args) {
        int count = 0;
        int i = 2;
        while (true) {
            if (isPrimeNumber(i) && isPrimeNumber(reverse(i)) && i != reverse(i)) {
                System.out.print(i + " ");
                count++;
                if (count % 10 == 0) {
                    System.out.println();
                }
            }
            i++;
            if (count == 100) {
                break;
            }            
        }
        
    }
}