Euler 项目 #12 的 Java 代码

Question

我正在研究 Project Euler 的问题 #12，具体内容如下:

The sequence of triangle numbers is generated by adding the natural numbers. So the 7th triangle number would be 1 + 2 + 3 + 4 + 5 + 6 + 7 = 28. The first ten terms would be:

1, 3, 6, 10, 15, 21, 28, 36, 45, 55, ...

Let us list the factors of the first seven triangle numbers:

1: 1

3: 1,3

6: 1,2,3,6

10: 1,2,5,10

15: 1,3,5,15

21: 1,3,7,21

28: 1,2,4,7,14,28

We can see that 28 is the first triangle number to have over five divisors.

What is the value of the first triangle number to have over five hundred divisors?

这是我到目前为止的代码，但控制台在运行时不会返回任何内容:

public class Euler12 {
    public static void main (String[] args) {
        int i = 1;
        int x = 2;
        boolean found = false;
        while (!found) {
            if (divisors(i) > 500) {
                System.out.println(i);
                found = true;
            }
            else {
                i +=x;
                x++;
            }
        }
    }

    public static int divisors (int n) {
        int counter = 0;
        for (int i = 1; i <= n; i++) {
            if (n % i == 0) counter++;
        }
        return counter;
    }
}

Answer 1

运行程序后，似乎它的运行时间非常长，看看你的算法，确实如此(我以前做过这个问题)。您需要优化“除数”

剧透

如果将 for (int i = 1; i <= n; i++) 改为 for (int i = 1; i*i <= n; i++)，将会大大减少执行时间。

更新:在不进行更改的情况下运行后，4 分钟内没有答案，这违反了 Project Euler 的一分钟规则。更改后，十秒内得到答复。享受吧:)