[Project Euler] Problem 2

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...

By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.

#include <iostream>
using namespace std;

int main(){
    int sum = 0;
    int a = 1, b = 2, c = 3;
    while(b < 4000000){
        sum += b;
        a = b+c;
        b = a+c;
        c = a+b;
    }
    cout << sum << endl;
    return 0;
}

求所有Fibonacc数列中值为偶数的数的和

观察数列，容易看出每隔两个数有一个偶数

所以，我们每三个数递推一次