Math Related Problem

[perito]

I'm trying to solve this problem

An irrational decimal fraction is created by concatenating the positive integers:

0.123456789101112131415161718192021...

It can be seen that the 12th digit of the fractional part is 1.

If dn represents the nth digit of the fractional part, find the value of the following expression.

d1 × d10 × d100 × d1000 × d10000 × d100000 × d1000000

Here is my code

public class Test 
{
	public static void main(String[] args)
	{
		String strNbr="";
		for(long i=1;i<1000000;i++)
			strNbr= strNbr + i;
		//Find the digits
		int d1=1,d10,d100,d1000,d10000,d100000,d1000000;
		int product=0;
		d10=Integer.parseInt(strNbr.substring(9, 10));
		d100=Integer.parseInt(strNbr.substring(99, 100));
		d1000=Integer.parseInt(strNbr.substring(999, 1000));
		d10000=Integer.parseInt(strNbr.substring(9999, 10000));
		d100000=Integer.parseInt(strNbr.substring(99999, 100000));
		d1000000=Integer.parseInt(strNbr.substring(999999, 1000000));
		product = d1 * d10 * d100 * d1000 * d10000 * d100000 * d1000000;
		System.out.println(product);
	}
}

I waited about 40 mins and the code showed no output
I know the loop is so long and there must be a better method to do this, but I cant think of a better method than using a string to store the number, since using a integer or double would lead to an extremely large number and would be very hard to locate d10-d100-d1000....

so what do you think I should do to solve this problem?

[Greyskull]

ur first mistake is on this line

strNbr= strNbr + i;

on this line, if u add a number on the current string it will be like

1, then 12, then 123, then 1234

so u will end up will something massive in the end hence the processing time is big. imo first store this number as an int then convert it to string later.

Regards,

[perito]

yea, thats exactly what i want
1 then 12 then 123... building a HUGE number, so I thought putting as an integer wont be a smart idea
look at the question
An irrational decimal fraction is created by concatenating the positive integers:

0.123456789101112131415161718192021...

the numbers are lining up near each other...

anyone have any idea how to solve this problem?

[perito]

ok here's how i solved it..
this is not a good way but it solved it
i looped till 100000 (a missing zero) which will not take so long to end, got the numbers d1,d10....d100000
so I still have d1000000 to find
since d1000000 is between 0 and 9
I tried all the numbers and found out that 210 is the correct answer

[Greyskull]

oh ic..sorz i miread the initial question, hehe