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Java小例子——穷举质数，求平方和，求质因子。

2024-07-07 08:14:52   231人阅读

求平方和

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public static void main(String[] args) throws IOException
    {
        int n;
        String s;
        BufferedReader buf;
 
        buf=new BufferedReader(new InputStreamReader(System.in));
 
        System.out.print("请输入一个自然数：");
        s=buf.readLine();
        n=Integer.parseInt(s);
 
        System.out.print("f(n)=1");
        for(int i=2;i<=n;i++)
            System.out.print("+"+i*i);
        System.out.print("="+Square(n));
 
    }
 
    public static long Square(int n)
    {
        long f=0;
        if(n<0)
            System.out.println("n<0，输入错误！");
        else if
            (n==1)f=1;
        else
            f=Square(n-1)+n*n;
        return f;
    }

 穷举质数

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public static void main(String args[])
    {
        int i,j;
        for(j=2;;j++) 
        {
            for(i=2;i<=j/2;i++)
            {
                if(j%i==0)
                    break;
            }
            if(i>j/2) 
            {
                System.out.println(j);
            }
        }
    }

 求质因子

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public static void main(String[] args)
    {
        int n = 0;
        String s = null;
        BufferedReader buf;
        buf=new BufferedReader(new InputStreamReader(System.in));
        System.out.print("请输入一个数：");
        try {
            s=buf.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        n=Integer.parseInt(s);
        int temp = n;
        for (int i = 2; i <= temp; i++)
        {
            if (!isPrime(i))
            {
                continue;
            }
            while (true)
            {
                if (temp%i == 0)
                {
                    temp = temp/i;
                    System.out.println(i);
                }
                else {
                    break;
                }
            }
        }
    }
    public static boolean isPrime(int n)
    {
        int i;
        for (i = 2; i <= n; i++)
        {
            if (n%i == 0)
            {
                break;
            }
        }
        if (i >= n)
        {
            return true;
        }
        else {
            return false;
        }
    }

 


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