显示质因数提示用户使用StackOfIntegers Java类进行整数运算

Question

So I have this assignment and I have been struggling any help or feedback would be welcomed :)

Problem

(Displaying the prime factors) Write a program that prompts the user to enter a positive integer and displays all its smallest factors in decreasing order. Using StackOfIntergers Class.

Here's what I have so far and the program compiles and runs but getting prime numbers instead of the prime factors.

package primefactors;
import java.util.Scanner;

public class PrimeFactors {
public static void main(String[] args) {
System.out.print("Enter a positive number: ");
Scanner scanner = new Scanner (System.in);
final int number = scanner.nextInt();
int count = 0;
StackOfIntegers stack = new StackOfIntegers();    

// Repeatedly find prime factors
for (int i = 2; i <= number; i++)
  if (isPrime(i)) {
    stack.push(i);
    count++; // Increase the prime number count
  }

// Print the prime factors
System.out.println("The prime numbers are \n");
final int NUMBER_PER_LINE = 10;

while (!stack.empty()) {
  System.out.print(stack.pop() + " ");

  if (stack.getSize() % NUMBER_PER_LINE == 0)
    System.out.println(); // advance to the new line
}
}

public static boolean isPrime(int number) {
// Assume the number is prime
boolean isPrime = true;

for (int divisor = 2; divisor <= number / 2; divisor++) {
  //If true, the number is not prime
  if (number % divisor == 0) {
    // Set isPrime to false, if the number is not prime
    isPrime = false;
    break; // Exit the for loop
  }
}

return isPrime;
}
}

* Update#2 * So I needed to just get the prime factor working so this is what I ended up with after researching some more & coding.

It works. Now I need to work on having the program show both prime factors and prime numbers in a nice list.

Thanks for the feedback & suggestions.

import java.text.MessageFormat;
import java.util.Scanner;

public class PrimeFactor {
    public static void main(String[] args) {
    System.out.print("Enter a positive number: ");
    Scanner scanner = new Scanner (System.in);
    int number = scanner.nextInt();
    int count;
    StackOfIntegers stack = new StackOfIntegers();    
    for (int i = 2; i<=(number); i++) {
        count = 0;
        while (number % i == 0) {
            number /= i;
            count++;
        }
            if (count == 0) continue;
              stack.push(i);
              count++;
    }
    System.out.println("The prime factors are \n");
    final int NUMBER_PER_LINE = 10;

     while (!stack.empty()) {
     System.out.print(MessageFormat.format("{0} ", stack.pop()));

    if (stack.getSize() % NUMBER_PER_LINE == 0)
     System.out.println(); // advance to the new line
    }
  }
} 

StackOfInterger Class

public class StackOfIntegers {
private int[] elements;
private int size;

/** Construct a stack with the default capacity 16 */
  public StackOfIntegers() {
    this(16);
 }

 /** Construct a stack with the specified maximum capacity */
 public StackOfIntegers(int capacity) {
   elements = new int[capacity];
 }

 /** Push a new integer into the top of the stack */
 public int push(int value) {
   if (size >= elements.length) {
     int[] temp = new int[elements.length * 2];
     System.arraycopy(elements, 0, temp, 0, elements.length);
     elements = temp;
   }

   return elements[size++] = value;
 }

 /** Return and remove the top element from the stack */
 public int pop() {
   return elements[--size];
 }   

 /** Return the top element from the stack */
 public int peek() {
   return elements[size - 1];
 }

 //whether the stack is empty */
 public boolean empty() {
   return size == 0;
 }

  /** Return the number of elements in the stack */
 public int getSize() {
   return size;
 }
 }

Answer 1

This works as described. When I ran it with 20, I got the following output: 19 17 13 11 7 5 3 2

These are all prime numbers. I'm not sure why you expect 5,3,2,2.

I believe the next step is to go through all of these prime numbers and see if they are prime factors of 20. This should be 5 and 2. To do this, you should iterate over the list and see if the input % (which is modulus) the number you're testing is equal to 0.

Answer 2

Try this it returns the 5 smallest prime factors of a given number if there is 5 prime factors. If you wanted to display two lists, one for primes and one for prime factors why not create two stacks and display separatly.

public class Temp2 {

public static void main(String[] args) 
{
    int number, integer, count = 0;
    StackOfIntegers stack = new StackOfIntegers();
    Scanner input = new Scanner(System.in);

    System.out.println("Enter a positive integer: ");
    integer = input.nextInt();

    //Find prime factors
    for (number = 2; number < integer; number++) 
    {
        if (isPrime(number) && integer % number == 0)
        { 
            stack.push(number);
            count++;
            if(count == 5) break;
        }
    }

    // Print the smallest prime factors in decreasing order
    System.out.println("The smallest prime factors of " + integer + " are ");

    while (!stack.empty()) 
    {
        System.out.print(stack.pop() + ", ");
    }
    System.out.println(); //Advance to the new line
}//ENDMAIN

public static boolean isPrime(int number) 
{
    for (int divisor = 2; divisor <= number / 2; divisor++) 
    {
        //If true, the number is not prime, return false
        if (number % divisor == 0) 
            return false;
    }
    return true;
}

}//ENDCLASS

Answer 3

A workable solution for this assignment question can be found here: http://www.besteduweb.com/assignment-solution-using-stack-of-integers-class.html

This is the 100% workable solution and works for me. Recommended 100%.