Permutation with BigInteger

Question

Permutation with BigInteger works fine upto 4 digits (3456 P 1234) when i give 5 digit input to n and r, it is not working. i have changed my input type as BigInteger n = scan.nextBigInteger();I edited my code as

`

    import java.math.BigInteger;
    import java.util.Scanner;

    public class cvic {
 public static void main(String[] args)
{   
Scanner scan = new Scanner(System.in);
System.out.print("Enter n and r: ");
BigInteger n = scan.nextBigInteger();
BigInteger r = scan.nextBigInteger();

System.out.println("nPr = "+fact(n).divide(fact(n.subtract(r))));
}
 static BigInteger fact(BigInteger num) {        
 BigInteger fa = BigInteger.ONE;      
for(BigInteger inte = BigInteger.ONE; inte.compareTo(num) <= 0; inte = inte.add(BigInteger.ONE)){            
fa = fa.multiply(inte);
    }        
    return fa;
    }
          }

`

Answer 1

You have an endless for loop, so your application never ends.

static BigInteger fact(BigInteger bv) {        
    BigInteger fa = BigInteger.ONE;      
    for(BigInteger inte = BigInteger.ONE; inte.compareTo(bv) <= 0; inte = inte.add(BigInteger.ONE)){            
        fa = fa.multiply(inte);
    }        
    return fa;
}

Answer 2

You have an infinite loop in your program:

for(inte.equals(1);inte.compareTo(BigInteger.ZERO)>=0;inte.add(BigInteger.ONE))

• inte.equals(1) always evaluates to true and as a bonus does nothing.
• inte.compareTo(BigInteger.ZERO) >= 0 is always true (that's why the for loop will never terminate) because inte is always equal to 1
• inte.add(BigInteger.ONE) - returns a new BigInteger and doesn't modify inte (BigInteger is an immutable class) - hence inte will always be equal to 1.

What you want is probably (I assume what you want is: calculate a factorial of bv):

while (inte.compareTo(bv) <= 0) {
  fa = fa.multiply(inte);
  inte = inte.add(BigInteger.ONE);
}

Correct handling of fact(0) is left as an exercise for the reader.

Answer 3

You need to bound your for loop by bv instead of zero. Also, you need to increment inte properly, as suggested in another answer.