JavaScript 用于 Project Euler 问题

Question

I am trying to solve Q10 from Project Euler. I am using JavaScript and Sieve of Atkins algorithm to solve the problem. When I run the code on browsers(Safari and FF) the browsers prompts that the script is unresponsive. Even if I let the script to continue I never got the answer. I know there are threads for the same Project Euler problem.

My questions would be:-

1.How far JavaScript is capable to solve such complex mathematical problems for browsers?

2.Is there any other environment where I can I test my JavaScript programs?

Thank you All.

Answer 1

The goal of project Euler is to get you thinking, mathematically. Think of brute forcing, and you will be stuck. Here is an implementation of the Sieve of Eratosthenes

---

function problem10() {

    var i, j, k, l = Math.floor((2000000-1)/2), a = [];
    for (i = 0; i < l; i++) {
        a[i] = true;
    } var m = Math.sqrt(2000000);
    for (i = 0; i <= m; i++) {
        if (a[i]) {
            j = 2 * i + 3;
            k = i + j;
            while (k < l) {
                a[k] = false;
                k += j;
            }
        }
    } var s = 2;
    for (i = 0; i < l; i++) {
        if (a[i]) {
            s += 2 * i + 3;
        }
    }
    return s;

}

var d1 = new Date().getTime();
var answer = problem10();
var d2 = new Date().getTime();

console.log('Answer:' + answer + ' time:' + (d2 - d1));

---

You can run it on the chrome developer's console (Ctrl + Shift + J). And guess what, it clocks 0.1 second.

Answer 2

1. I would have thought as capable as any other - JavaScript implementations have been optimised a lot in recent years thanks to increased used in the web.

2. You can use either node.js or CScript (a command line version of the Windows Script host - this is supplied as part of Windows).

If I remember my implementation of that question (in Python) was significantly slower than I thought it would be. The chances are the slowness is due to your algorithm rather than the language.

Answer 3

function problem10(){

    var a = 0;

    function isPrime(n){
        var i = 2;
        var b = true;
        while(i<=Math.sqrt(n) && b){
            b = n%i===0?false:true;
            i++;
        }
        return n<2?false:b;
    }

    for(i=0;i<2000000;i++){
        if(isPrime(i)){
            a+=i;
        }
    }
    return a;

}

Answer 4

You could try testing your implementation on node.js .

However, I would bet that you have a problem with your code. JavaScript in a modern browser is pretty quick (and generally you should get Project Euler answers very quickly; it's not designed to require high amounts of computing power).