Project Euler #8: Largest product in a series - Hacker Rank Program

Problem Statement

_{This problem is a programming version of Problem 8 from projecteuler.net}
Find the greatest product of K consecutive digits in the N digit number.
Input Format
First line contains T that denotes the number of test cases.
First line of each test case will contain two integers N & K.
Second line of each test case will contain a N digit integer.
Output Format
Print the required answer for each test case.
Constraints
1≤T≤100
1≤K≤7
K≤N≤1000
Sample Input

2
10 5
3675356291
10 5
2709360626

Sample Output

3150
0

 MY SOLUTION:

import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    public static void main(String[] args) {
        Scanner s=new Scanner(System.in);
        int t=s.nextInt();
        while(t!=0)
            {
            int k=s.nextInt();
            int n=s.nextInt();
            String a=s.next();
            int i,j,count=0,max=0,sum=1;
            j=n;
            while(j!=k)
            {
                 String b=a.substring(count,j);
                 count++;
                 j++;
                sum=1;
               for(i=0;i<b.length();i++)
                {
                 sum=sum*Character.getNumericValue(b.charAt(i));
               }
               if(max<sum)
               max=sum;
            }
            System.out.println(max);
            }
            t--;
        }
    }