Java function to find numbers

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Java function to find numbers

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#1 by (4 votes)
#2 by (1 votes)

2

I am trying to write a program to show the list of coquette numbers cousins of a number of figures entered by the user (between 2 and 15 ). I already have the functions of capicúa and cousin.

But the problem I have is how to make the function so that you entered that number from 2 to 15 , print the numbers.

If the entry is 2 , I do (2/2)*10 and up to 99 , making it print the 11 (only cousin and capicúa 2 figures).

But I do not know how to materialize it in a loop.

java

asked by Fernando 30.10.2016 в 06:50

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2 answers

1

Based on your comment, as you already have a code to detect if it is a cousin and another to know if it is capicúa, I will focus on how to do the range to make the filter, as you say, if you enter a 2 filter the numbers of two figures, if they enter a 3 filter those of three, and so on.

int numero = 2;//Aquí el número que quieras, por ejemplo un 2, sería el que introducirías por pantalla

if(numero >= 2 && numero <= 15){

    double empezar = Math.pow(10,numero); //Aquí empezará el bucle (10 para el 2, 100 para el 3, etc...)

    double acabar = Math.pow(10, numero) - 1; //Obtenemos 99, 999, 9999...

    for(int i = empezar; i <= acabar; i++){
        if((esCapicua(i) == true) && (esPrimo(i) == true)){
            System.out.println("El número " + i + "es capicua");
        }
    }
}

answered by 30.10.2016 в 21:17

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score 4 · Accepted Answer

For that I need a function that gets every digit. In the following link, you can see a pretty good answer.

link

public static int obtener_digito(int numero, int posicion)
{
    return (numero/(int)Math.pow(10,posicion))%10;
}

Using this function, you can check one by one, from the outside to the inside to see if the digits are the same.

public static Boolean es_capicua(int numero)
{
    Boolean es_capicua_actual = true;
    int longitud=(int) Math.log10(numero);
    for (int i = 0; i <= longitud/2; i++)
    {
        int izquierda = obtener_digito(numero,i);
        int derecha = obtener_digito(numero,longitud-i);
        if( izquierda!=derecha )
        {
            es_capicua_actual = false;
            break;
        }
    }
    return es_capicua_actual;
}

A function is also needed to know if a number is prime. Luckily I found her, chewing a little about the site.

link

The only problem is that it is in C, but I convert it to Java.

public static Boolean es_primo(int numero)
{
    Boolean es_primo_actual = true;
    if(numero<2)
    {
        es_primo_actual = false;
    }
    else
    {
        for(int x=2; x*x<=numero; x++)
        {
            if( numero%x==0 ){es_primo_actual = false;break;}
        }
    }
    return es_primo_actual;
}

Solving the main problem:

On the internet I found how to ask for data by keyboard. A scanner is declared, then numbers are required from the user, and finally the scanner is closed.

link

System.out.print ("Ingrese un numero del 2 al 15:\n");
Scanner teclado = new Scanner(System.in);
int n = teclado.nextInt();
teclado.close();

Also, how to show something on the screen.

link

System.out.print(i);

Then, you can check with a if if the number is between 2 and 15 , this way. Finally, check that the numbers that are going to show are capicúas, cousins, and have a certain number of figures. For that use Math.pow , to generate a number that is power of 10 , that is, we use the decimal number system.

if(n>=2 & n<=15)
{
    int potencia_10_actual=(int) Math.pow(10,n-1);
    int potencia_10_siguiente=10*potencia_10_actual;
    for(int i=potencia_10_actual;i<potencia_10_siguiente;i++)
    {
        if( es_primo(i) && es_capicua(i) )
        {
            System.out.print (i+" ");
        }
    }
}