Project Euler Forum

3, 99 are correct.
5, 50 are wrong - 5 is actually relatively far off.

jaap wrote:3, 99 are correct.
5, 50 are wrong - 5 is actually relatively far off.

I think I found the problem, is 474 correct for sqrt 5?

Nevermind, it must have been because I got the answer.

PurpleBlu3s wrote:I think I found the problem, is 474 correct for sqrt 5?

It's better, but still false.

Francky wrote:

PurpleBlu3s wrote:I think I found the problem, is 474 correct for sqrt 5?

It's better, but still false.

Yes, 473. :>

It was an issue with rounding.

So I have written an algorithm for problem 80, and I ended up with the wrong answer of 40909. What I don't get about this is that I have the correct sum for the square root of 2, and I also have the correct number for the square root of 99. Am I missing something? I sum without the perfect squares, and I include the first number for the digital sum. I can't see where my algorithm is going wrong, and yet the sum keeps getting rejected. Any suggestions?

Here's the forum thread for problem 80: viewtopic.php?f=50&t=1198

I suspect you're making a mistake that has been mentioned in some posts there.

I don't think I am. I know that my method, which is a binary go by digit, won't do rounding, and I went out super far to double check that. I am including the first digit, so that's not the problem either. I can't get why I would be getting the right number for sqrt(99), but not the right total sum.
Just to check, the digit sum for 99 is 446, right?

cptroot wrote:I don't think I am. I know that my method, which is a binary go by digit, won't do rounding, and I went out super far to double check that. I am including the first digit, so that's not the problem either. I can't get why I would be getting the right number for sqrt(99), but not the right total sum.
Just to check, the digit sum for 99 is 446, right?

Yes, but you have to have every square root digital sum correct not just 2 and 99. Check if you are getting it right for other values - it's likely some are wrong.

Does anybody have a list of sums they could pm me? I'm interested in finding out the right answer, but I have no idea where my bug is, especially because it seems to be getting so much right.

cptroot wrote:Does anybody have a list of sums they could pm me? I'm interested in finding out the right answer, but I have no idea where my bug is, especially because it seems to be getting so much right.

If you pm me your sums I can compare them to mine.

Should I be accounting for any leading zeros that will fall off when the rightmost digits are isolated? For instance if the square root of N is 5.02, is the first digit 0 or 2?

There is already a thread for problem 080 here.
In it you will find the answer to your question, which is that the first digit in your example is actually 5.

Topics merged.

I think it's ridiculously stubborn on the part of the mods to refuse to alter the wording of the question. Many people have been thrown off by the phrase 'decimal digits' which is assumed to imply the digits after the decimal point. If you insist on retaining the current formulation of the question, the least you can do is include a note about this.