Resistance- How do i fix this code ?

algorithm
c
resist
runtime-error

#1

This is the


[1] i have written for the [resistance][2] problem.

I have written recursive functions to calculate numerator and denominator. In the end I am reducing the fraction by recursively dividing numerator and denominator by their gcd until the gcd becomes 1.

As per the formula 1/R = 1/R1 + 1/R2 ,therefore at any given time 1/R(n) = 1/R(n-1) + 1/2 

where R(n) is the equivalent resistance when there are n blocks.
![alt text][3]

Say  R(n-1) = A/B , thus 1/R(n) = B/A + 1/2 
Thus numerator of R(n) = 2*A and denominator = 2*B + A 

I have written two functions for calculating these.

    //numerator calculator
    

long  int num_calc(long  int n)

{
	if(n==1)
	return 1;
	
	else return 2*num_calc(n-1);
}



    //denominator calculator
    

long  int den_calc(long  int n)

{
	if(n==1)
	return 1;
	
	else return 2*den_calc(n-1) + num_calc(n-1);
}

After that I keep reducing the fraction by continuously, dividing numerator and denominator by their gcd, until the gcd is 1.

    //calculates the reduced form of the fraction
    //num is the numerator and den is the denominator in the code

void lowest_fraction(long  int a, long  int b)

{
	if(gcd(a, b)==1)
	{
		num = a;
		den = b;
	}
	
	else(lowest_fraction((a/gcd(a,b)), (b/gcd(a,b))));
	
}



It works for n<29 but I start getting errors when n >=29

Can anyone please suggest any fixes for the code ?


  [1]: http://www.codechef.com/viewsolution/3497356
  [2]: http://www.codechef.com/problems/RESIST#comment-74413
  [3]: http://discuss.codechef.com/upfiles/resistance_1.png

#2

can you explain your logic clearly?