CODEWITHSUNDEEP
javaeclipserecursion
earora4498
earora4498

Reputation: 127

Sum of Factorials Error

I'm trying to write a program that calculates the sum of a factorials up to a number. So if I gave it 3 it would return 3! + 2! + 1!. Here is my code so far:

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


public class sumOfFactorial { 

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int n = input.nextInt();
        System.out.println(sum(n));

    }

    public static BigInteger sum(int n) {
        return factorial(n).add(sum(n-1));
    }

    public static BigInteger factorial(int n) {
        BigInteger x = BigInteger.valueOf(n);
        if (n == 1) return BigInteger.ONE;
        else return x.multiply(factorial(n-1)); //error occurs here
    }
}

For some reason it gives me a Stack Overflow error at the indicated spot. How can I fix this?

Upvotes: 0

Views: 141

Answers (2)

BevynQ
BevynQ

Reputation: 8269

one of your problems is here

public static BigInteger sum(int n) {
    return factorial(n).add(sum(n-1));
}

try

public static BigInteger sum(int n) {
    if(n > 1){
      return factorial(n).add(sum(n-1));
    } else if (n < 0){
      throw new IllegalArgumentException("factorials are not defined for negative integers");
    } else {
      return BigInteger.ONE;
    }
}

Upvotes: 2

rgettman
rgettman

Reputation: 178263

You are nesting two recursive methods, sum and factorial. However, your sum recursive method doesn't have a base case. Like factorial, it must have a base case. Make sure sum stops recursing at a base case, which in your case appears to be n equals 1.

Upvotes: 3

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