Java中euler项目#14的运行时间太长

我的Euler Project 14代码如下.我已经运行此代码超过3个小时的输出结果,它似乎是无限的.当我测试单个数字(如11,27)时,它将快速输出collat​​z链数：14和111.但我不知道为什么它不能输出1000000数字的最大链数.

/*Problem 14
 * The following iterative sequence is defined for the set of positive integers:
 *          n -> n/2 (n is even)
 *          n -> 3n + 1 (n is odd) 
 * Using the rule above and starting with 13, we generate the following sequence:
 *               13 -> 40 -> 20 -> 10 -> 5 -> 16 -> 8 -> 4 -> 2 -> 1
 * It can be seen that this sequence (starting at 13 and finishing at 1) contains 
 * 10 terms. Although it has not been proved yet (Collatz Problem), it is thought 
 * that all starting numbers finish at 1.
 * 
 * Which starting number, under one million, produces the longest chain?
 * 
 * NOTE: Once the chain starts the terms are allowed to go above one million.
 */
package number;  
public class LongestCollatzSequence {
    public static int collatzNum(int n){
        int count = 0;
        while(n != 1){
            if(n%2 == 0)
                n = n/2;
            else 
                n = 3*n + 1;
            count++;
        }
        return count;
    }
    public static void main(String[] args) {
        int max = 0;
        for(int i = 10; i <= 1000000; i++){
            if(collatzNum(i) > collatzNum(max))
                max = i;
        }
        System.out.println(max);
    }
}

此外,我转向(int i = 10; i< = 1000000; i)to for(int i = 10; i< = 10; i),这么短的数字列表,它仍然一直在运行没有输出.我的代码出了什么问题？ 这是另一个人的决议,rianjs.net的代码是：

public class Problem014
{
    public static void main(String[] args)
    {
        long begin = System.currentTimeMillis();
        LinkedList<Long> list = new LinkedList<Long>();
        long length = 0;
        int res = 0;
        for(int j = 10; j < 1000000; j++){
            long i = j;
            while (i != 1){
                if (i % 2 == 0){
                    i /= 2;
                    list.add(i);
                }
                else{
                    i = (3 * i) + 1;
                    list.add(i);
                }
            }
            if(list.size() > length){
                length = list.size();
                res = j;
            }
            list.clear();
        }
        long end = System.currentTimeMillis();
        System.out.println(res+" with chain size: "+ length);
        System.out.println(end-begin + "ms");
    }
}

他的代码运行良好,我想知道为什么我的代码无法获得输出以及两个分辨率的差异是什么？

解决方法:

你的collat​​zNum函数的参数int n将溢出值113383.正如你所看到的,另一个实现使用一个long变量作为临时值.

除此之外,您可以通过不为每个循环迭代计算collat​​zNum(max)来优化代码,但仅当max实际更改时,在这种情况下,您已经将新的collat​​zNum(max)作为来自collat​​zNum的返回值(一世).

标签：collatz,java,algorithm
来源： https://codeday.me/bug/20190723/1509833.html