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.

Javascript Function to Compute the Sum of Even Fibonacci Numbers

Fibonacci Numbers can be computed iterated. Then we need to pick those even Fibonacci numbers. The following is a Javascript function to sum up the Fibonacci numbers less than a maximum value.

The time complexity is obvious O(N) for a iterative Fiboancci sequence where N is the number of Fiboancci numbers less than the threshold. The space complexity is O(1) constant.

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function SumOfFibLessThan(max) {
    let a = 1, b = 2;
    let sum = 0;
    while (a <= max) {
        if (a % 2 === 0) {
            sum += a;
        }    
        let c = a + b;
        a = b;
        b = c;
    }
    return sum;
}
 
console.log(SumOfFibLessThan(4000000));

function SumOfFibLessThan(max) {
    let a = 1, b = 2;
    let sum = 0;
    while (a <= max) {
        if (a % 2 === 0) {
            sum += a;
        }    
        let c = a + b;
        a = b;
        b = c;
    }
    return sum;
}

console.log(SumOfFibLessThan(4000000));

Answer is: 4613732.

–EOF (The Ultimate Computing & Technology Blog) —