项目欧拉,问题2- Java

Question

我是一个相对较新的java程序员,而且我现在一直在修补这个程序,现在我已经陷入困境了.我希望你能帮助我.

所以该程序应该满足以下要求:

Fibonacci序列中的每个新术语都是通过添加前两个术语生成的.从1和2开始,前10个术语将是:

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

通过考虑Fibonacci序列中的值不超过四百万的项,找到偶数项的总和.

这是我的代码:

    //Generates Fibonacci sequence
    while (fibNum < 144)
    {
        int lastValue = (Integer) fibList.get(fibList.size()-1);
        int secondToLastValue = (Integer) fibList.get(fibList.size()-2);

        fibNum = secondToLastValue + lastValue;

        if (fibNum < 144)
        {
            fibList.add(fibNum);
        }

    //Picks out the even numbers from limitFibList
    for (int i = 0; i < fibList.size(); i++)
    {
        if ((Integer) fibList.get(i) % 2 == 0)
        {
            evenNumsFibList.add(fibList.get(i));
        }
    }

    //Sums up the total value of the numbers in the evenNumsFibList
    for (int i = 0; i < evenNumsFibList.size(); i++)
    {
        sum += (Integer) evenNumsFibList.get(i); 
    }

......这是我得到的输出:

Fibonacci sequence list: [1, 2, 3]
Size of the Fibonacci list: 3
Even Numbers list: [2]
Total sum of even numbers: 2

Fibonacci sequence list: [1, 2, 3, 5]
Size of the Fibonacci list: 4
Even Numbers list: [2, 2]
Total sum of even numbers: 6

Fibonacci sequence list: [1, 2, 3, 5, 8]
Size of the Fibonacci list: 5
Even Numbers list: [2, 2, 2, 8]
Total sum of even numbers: 20

Fibonacci sequence list: [1, 2, 3, 5, 8, 13]
Size of the Fibonacci list: 6
Even Numbers list: [2, 2, 2, 8, 2, 8]
Total sum of even numbers: 44

Fibonacci sequence list: [1, 2, 3, 5, 8, 13, 21]
Size of the Fibonacci list: 7
Even Numbers list: [2, 2, 2, 8, 2, 8, 2, 8]
Total sum of even numbers: 78

Fibonacci sequence list: [1, 2, 3, 5, 8, 13, 21, 34]
Size of the Fibonacci list: 8
Even Numbers list: [2, 2, 2, 8, 2, 8, 2, 8, 2, 8, 34]
Total sum of even numbers: 156

Fibonacci sequence list: [1, 2, 3, 5, 8, 13, 21, 34, 55]
Size of the Fibonacci list: 9
Even Numbers list: [2, 2, 2, 8, 2, 8, 2, 8, 2, 8, 34, 2, 8, 34]
Total sum of even numbers: 278

Fibonacci sequence list: [1, 2, 3, 5, 8, 13, 21, 34, 55, 89]
Size of the Fibonacci list: 10
Even Numbers list: [2, 2, 2, 8, 2, 8, 2, 8, 2, 8, 34, 2, 8, 34, 2, 8, 34]
Total sum of even numbers: 444

Fibonacci sequence list: [1, 2, 3, 5, 8, 13, 21, 34, 55, 89]
Size of the Fibonacci list: 10
Even Numbers list: [2, 2, 2, 8, 2, 8, 2, 8, 2, 8, 34, 2, 8, 34, 2, 8, 34, 2, 8, 34]
Total sum of even numbers: 654

显然我的while循环导致了我的问题,但我不知道如何解决它.

非常感谢你的帮助,

哈克

Answer 1

如果你仔细看一下你实际需要的Fibonacci序列中的数字(只有偶数需要求和),你会看到一个模式:

0  1  1  2  3  5  8  13  21  34  55  89  144 ...
-  O  O  E  O  O  E   O   O   E   O   O    E

请注意,从0开始的每个第3个数字都是偶数.因此,如果计算每第三个Fibonacci数,则可以消除任何均匀性检查.再看一下这个序列,你可以看到,如果你现在看到的k是甚至斐波那契数,并且j是前一个,下一个偶数斐波那契数n可以通过以下方式获得:

n = 4k + j

所以在Java中,你可以尝试这样的事情:

int j = 0;
int k = 2;
int sum = j+k;

while (k < LIMIT) {
    int tmp = 4*k + j;
    sum = sum + tmp;
    j = k;
    k = tmp;
}

Answer 2

看起来你错过了while循环上的小括号.所以其他for人在其中运行.

所以:

while (fibNum < 144)
    {
        int lastValue = (Integer) fibList.get(fibList.size()-1);
        int secondToLastValue = (Integer) fibList.get(fibList.size()-2);

        fibNum = secondToLastValue + lastValue;

        if (fibNum < 144)
        {
            fibList.add(fibNum);
        }
    }

    //Picks out the even numbers from limitFibList
    for (int i = 0; i < fibList.size(); i++)
    {...