欧拉8号项目：奇怪的问题

Question

我已经尝试解决Project Euler 问题8，我相信我有正确的方法，但是由于某些原因，在以下代码中，当i=494 。 我相信线是38。
PS。 字符串的长度也是1000，如调试器所示。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace euler8
{
    class Program
    {
        static void Main(string[] args)
        {
           const String candidate =   "73167176531330624919225119674426574742355349194934"+
                                      "96983520312774506326239578318016984801869478851843"+
                                      "85861560789112949495459501737958331952853208805511"+
                                      "12540698747158523863050715693290963295227443043557"+
                                      "66896648950445244523161731856403098711121722383113"+
                                      "62229893423380308135336276614282806444486645238749"+
                                      "30358907296290491560440772390713810515859307960866"+
                                      "70172427121883998797908792274921901699720888093776"+
                                      "65727333001053367881220235421809751254540594752243"+
                                      "52584907711670556013604839586446706324415722155397"+
                                      "53697817977846174064955149290862569321978468622482"+
                                      "83972241375657056057490261407972968652414535100474"+
                                      "82166370484403199890008895243450658541227588666881"+
                                      "16427171479924442928230863465674813919123162824586"+
                                      "17866458359124566529476545682848912883142607690042"+
                                      "24219022671055626321111109370544217506941658960408"+
                                      "07198403850962455444362981230987879927244284909188"+
                                      "84580156166097919133875499200524063689912560717606"+
                                      "05886116467109405077541002256983155200055935729725"+
                                      "71636269561882670428252483600823257530420752963450";

            long max = 0;
            int length = candidate.Length;
            for (int i = 0; i < length - 13; i++)
            {
                string substring = candidate.Substring(i, i + 13);

                int [] x = new int [13];
                for(int j = 0; j<13; j++)
                    x[j]= int.Parse(substring[j].ToString());

                long product = 1;
                for (int k = 0; k < 13; k++)
                    product = product * x[k];

                if (product > max)
                    max = product;

            }

            Console.WriteLine(max.ToString());



        }
    }
}

有人发现这个问题吗？

Answer 1

看来这是由于对.SubString()工作方式有误解。

string substring = candidate.Substring(i, i + 13);

最有可能应该是：

string substring = candidate.Substring(i, 13);

.SubString()是： .SubString(startPosition, length)因此，添加i + 13不会为您带来下13个字符，而是从起始位置i开始的下i + 13字符。

Answer 2

String.Substring需要一个开始位置加上一个length ，而不是结束位置。

所以就用

string substring = candidate.Substring(i, 13);