Project Euler Problem8. I can't seem to find the fault in this code. What am I doing wrong?

Question

Question: The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.

73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450

Find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?

In my solution, I've used StringTokenier to first break the number into parts from places wherever a 0 is found. Then I've used nested loops to calculate the product of each sequence of of 13 (or less) digits accordingly.

import java.util.*;
public class Project_Euler_8
{
    public static void main(String num)
    {
        StringTokenizer st= new StringTokenizer(num, "0");
        String arr []= new String [1000];
        int i=0;
        while(st.hasMoreTokens())
        {
            arr[i++]=st.nextToken();
        }

        long product=1L;
        long temp;

        for(int j=0;j<i;j++)
        {
            if(arr[j].length()<=13)
            {
                temp=findProduct(arr[j], 0, arr[j].length());
                 if(temp>product)
                    {
                        product=temp;
                    }
            }
            else
            {
                int end=13;
                int start=0;
                while(end<=arr[j].length())
                {
                    temp=findProduct(arr[j], start, end);
                    start++;
                    end++;

                    if(temp>product)
                    {
                        product=temp;
                    }
                }
            }
        }
        System.out.println(product);

    }

    public static long findProduct(String str, int start, int end)
    {
        long product=1L;
        for(int i=start;i<end;i++)
        {
            product=product*(Long.valueOf(str.charAt(i)));
        }
        return product;
    }
}

Answer 1

This should work, no need to worry about zeros. Java long (64 bits) is enough for 13 decimal digits.

public class Product1000 {
    static String numbers =
        "73167176531330624919225119674426574742355349194934"+
        "96983520312774506326239578318016984801869478851843"+
        "85861560789112949495459501737958331952853208805511"+
        "12540698747158523863050715693290963295227443043557"+
        "66896648950445244523161731856403098711121722383113"+
        "62229893423380308135336276614282806444486645238749"+
        "30358907296290491560440772390713810515859307960866"+
        "70172427121883998797908792274921901699720888093776"+
        "65727333001053367881220235421809751254540594752243"+
        "52584907711670556013604839586446706324415722155397"+
        "53697817977846174064955149290862569321978468622482"+
        "83972241375657056057490261407972968652414535100474"+
        "82166370484403199890008895243450658541227588666881"+
        "16427171479924442928230863465674813919123162824586"+
        "17866458359124566529476545682848912883142607690042"+
        "24219022671055626321111109370544217506941658960408"+
        "07198403850962455444362981230987879927244284909188"+
        "84580156166097919133875499200524063689912560717606"+
        "05886116467109405077541002256983155200055935729725"+
        "71636269561882670428252483600823257530420752963450";

    static int DIGITS=13;
    static long calcProduct(int from) {
        long x=1;
        for (int i=0; i <DIGITS; ++i) {
            x*=numbers.charAt(from+i)-'0';
        }
        return x;
    }
    public static void main(String[] args) {
        int l=numbers.length()-DIGITS;
        long best=0;
        int besti=-1;
        for (int i=0; i < l; ++i) {
            long p=calcProduct(i);
            if (best<p) {best=p;besti=i;}
        }
        System.out.printf("best=%d for digits %s\n", best, numbers.substring(besti, besti+DIGITS));
    }
}