collatz.cpp

/*
 * main.cpp
 *
 *  Created on: Oct 23, 2013
 *      Author: david
 */

#include <iostream>
#include <map>
#include <stdio.h>


std::map<unsigned long, int> collatz;


int Collatz(unsigned long n){
	if(!collatz[n]){
		if(n % 2 == 0){
			collatz[n] = Collatz(n/2);
		} else {
			collatz[n] = Collatz(3*n + 1);
		}
	}
	return collatz[n] + 1;
}

int biggest = 0;
int chain = 0;


void find_biggest(){
	for(unsigned long i = 0; i < collatz.size(); i++){
		int value = collatz[i];
		if(value > chain){
			biggest = i;
			chain = value;
		}
	}
}

int main(){
	collatz[1] = 1;

	for(int j = 10000; j > 0; j--){
		Collatz(j);
	}
	find_biggest();
	fprintf(stdout, "Biggest:%i Chain:%i\n", biggest, chain);
	return 0;
}