Check if the number a perfectSquare (number has more than 15 digits)

Question

I wish to calculate the square root of a number which had more than 15 digits if possible for 100 digits it would be great

number like 100000000000000

Currently i am using C with integer as data type

int IsPerfectSquare(int number)
{

   if (number< 0)

   return 0;

   int root = (round(sqrt(number)));

    if(number == (root * root))

    {        
       return 1;    
    }    
    else
    {        
      return 0;    
    }
}

But does double or long double can hold 15 digits or more

Language is no bar. I can code in C# as well

Thanks :)

Getting the square root is the hard bit. Check [this thread](http://stackoverflow.com/questions/3432412/calculate-square-root-of-a-biginteger-system-numerics-biginteger) for a possible solution. — Matthew Watson, Apr 13 '13 at 15:20
I think you shouldn't ask questions like this [during the competition](https://code.google.com/codejam/contest/2270488/dashboard#s=p2). — svick, Apr 13 '13 at 16:04

score 2 · Accepted Answer · answered Apr 13 '13 at 15:19

2

In C# you can use decimal to get up to 29 digits and BigInteger to get arbitrarily many digits.

However, you'll need a different technique to tell if a 100 digit BigInteger is a perfect square, as there isn't an off-the-shelf "root" function that I'm aware of.

answered Apr 13 '13 at 15:19

Eric Lippert

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You could always use a variation of the babylonian method to converge on the square root of the number: http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Babylonian_method – Patashu Apr 13 '13 at 15:25
@Patashu: There are lots of ways to compute the square root of an integer. See the linked duplicate answers for some examples. – Eric Lippert Apr 13 '13 at 15:29

taocp · Answer 2 · 2013-04-13T15:24:28.333

0

In C++, You can check how many bigs long double can hold by using the following function:

 std::cout << std::numeric_limits<long double>::digits10 << std::endl;

If you really want to deal with numbers with 100 digits, you need to code your own BigInteger class.

edited Apr 13 '13 at 15:24

answered Apr 13 '13 at 15:18

taocp

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score 0 · Answer 3 · answered Apr 13 '13 at 15:22

0

The size of an integer in C is platform-dependant, so there is no guarantee of how many digits it can hold. You can look into the GNU Multiple Precision math library for dealing with big numbers in C.

answered Apr 13 '13 at 15:22

Kninnug

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Check if the number a perfectSquare (number has more than 15 digits)

3 Answers3