Comments on: Project Euler in F# – Problem 45

By: DFectuoso

DFectuoso — Thu, 05 Mar 2009 00:07:12 +0000

Thanks, the “The solution to the problem is greater than I could imagine” was they key i needed to find my error

By: dennys

dennys — Mon, 01 Sep 2008 20:21:44 +0000

Good thingking, thanks for the hints. I’m not like the idea that generate three large sequences. Your idea is much better. I’m not use bignums, the solution is an integer of 32 bits. My C++ code:

#define EPS 1e-10
#define MAX 100000

int hex(int n){ return (int) n*(2*n-1);}
bool is_pentagonal(int x){
        double _n;
        int n;
	_n = (sqrt(24.0*x + 1.0) + 1.0)/6.0;
	n = (int) _n;
	return (fabs(_n-(double)n)<EPS);
}
main(){
	int j, hexagonal;
	for(j=144;j%d\n",hexagonal);
			break;
		}
	}

}

By: Chris Smith

Chris Smith — Tue, 22 Apr 2008 20:46:42 +0000

I think this approach is great! I’ve been working on Problem 45 myself using the ‘generate three infinite sequences, and increment until they are all equal’ approach. However, as you discovered, the search space is a tad large…