Skip to main content

Prime Factors of a given number

Write a program to find all prime factors of a given number. 


The program should print the factors of a number which are prime. 

One way of writing this is 
  1. If the number is divisible by 2, repeatedly divide the number by 2 until it is no longer divisible by 2. Print 2 as a factor if number is divisible.
  2.  In a loop for values of i from 3 to n in steps of 2, find if a number is divisible by i. If yes repeatedly divide by i as long as number is divisible. 
  void printFactors(int num){
          if(num%2==0){
            System.out.println("2 ");
            while (num%2==0)
             num = num/2;
          }
        
          for(int i=3;i<=num;i+=2){
               if(num%i==0){
                    System.out.println(i);
                  while(num%i==0)
                     num = num/i;
               }
          }

     }
Here is the complete program.



import java.util.Scanner; 
class PrimeFactors{
     void printFactors(int num){
          if(num%2==0){
            System.out.println("2 ");
            while (num%2==0)
             num = num/2;
          } 
          for(int i=3;i<=num;i+=2){
               if(num%i==0){
                    System.out.println(i);
                  while(num%i==0)
                     num = num/i;
               } 
          }

     }

     public static void main(String args[]){
         PrimeFactors pf = new PrimeFactors();
         int n;
         Scanner scanner = new Scanner(System.in);
         n  = scanner.nextInt();
         pf.printFactors(n);
     }
}
Labels:

Comments

Post a Comment

Popular posts from this blog

Recursion - factorial

Write a recursive function to find factorial of a number. According to definition,    n! = n*(n-1)! Yes, the definition is recursive. Which makes our coding easier. Recursive function A function which invokes or calls itself is called a recursive function. Just like the definition given above, you write factorial(n-1) within factorial(int n) function. Now you may wonder, won't this type of function cause an infinite loop? It does, unless you create a base condition in which there is no recursive call. In this example, n = 0 is the base condition. So 0! is 1 and if n is 0 we just return 1. Here is how we have to write our recursive function for factorial. if n >0 return n* factorial(n-1) if n =0 return 1 Wow, so concise! And recursive functions are often deceptively small. Here is our complete function in Java int factorial ( int n ){ if ( n == 0 ) return 1 ; return n * factorial ( n - 1 ); }
Post a Comment
Read more

Reverse string using recursion

While we are at it, let us write another recursive function - a function to reverse the characters of a string. Write a recursive function to reverse a string  To reverse a string, we can use this algorithm If the string is not empty return substring of last n-1 characters +first character To reverse the string we need to move the characters from begining of string to end of string. We take the string, some how we reverse last n-1 characters and then add the first character to the end. Let us look at an example of reversing the 5 letter string Hello  Reverse Hello Reverse ello + H reverse llo+e reverse lo+l reverse o+l reverse ""+o The last call just returns the empty string. This returned value is available to previous call. This will return o. Then we go to the previous call of function which will add l to this and return lo. Then we move up the function stack and add l to this lo and return llo. And so on. Here is the code   ...
Post a Comment
Read more

Binary numbers in Java

Write a program to add two binary numbers in Java. Before you start thinking about long binary arithmetic operation, be happy for the fact that Java has inbuilt mechanism for writing binary literals and displaying a number in binary. If we prefix a number with 0b, the number will be treated as binary literal.    e.g. int num1 = 0b1110;/* binary value*/ int num2 = 0b0001; To convert a number to binary - or to display a number in binary, we can use the method toBinaryString() in Integer class.  int a = 10; String st = Integer.toBinaryString(a);/*st is 1010*/ Now we just write a simple program to add two binary literals and display the answer in binary. public class Demo { public static void main ( String args []) { int m = 0 b110011 ; int n = 0 b101100 ; int ans = m + n ; System . out . println ( "The sum of two numbers is " + Integer . toBinaryString ( ans )); } } By the way, do y...
Post a Comment
Read more