//ProjectEuler/C++/Problem2.cpp
//Matthew Ellison
// Created: 9-28-18
//Modified: 9-28-18
//The sum of the even Fibonacci numbers less than 4,000,000


#include <iostream>
#include <vector>
#include <chrono>


int main(){
	unsigned long fullSum = 2;	//Holds the sum of all the numbers
	std::vector<unsigned long> fib = {1, 1};	//Holds the Fibonacci numbers
	unsigned long nextFib = 2;	//Holds the next Fibonacci number

	std::chrono::high_resolution_clock::time_point startTime = std::chrono::high_resolution_clock::now();	//Start the timer
	while(nextFib < 4000000){
		//If it is an even number add it to the sum
		if(nextFib % 2){
			fullSum += nextFib;
		}
		//Move all the fib numbers down and calculate the next one
		fib.at(0) = fib.at(1);
		fib.at(1) = nextFib;
		nextFib = fib.at(1) + fib.at(0);
		//You could do this keeping all the fib numbers and sum at the end,
		//but this way will be faster because you are only handling every number twice
		//and you don't have to expand the vector
	}
	//Calculate the time needed for the algorithm
	std::chrono::high_resolution_clock::time_point endTime = std::chrono::high_resolution_clock::now();	//End the timer
	std::chrono::high_resolution_clock::duration dur = std::chrono::duration_cast<std::chrono::nanoseconds>(endTime - startTime);

	//Print the resultss
	std::cout << "The sum of the even Fibonacci numbers less than 4,000,000 is " << fullSum
			<< "\nIt took " << dur.count() << " nanoseconds to run this algorithm" << std::endl;

	//Pause before ending
	std::cin.get();
	return 0;
}