The problem is to find out the squares between two numbers, inclusive of the numbers. The two numbers are in the range between 1 and 109.

long numberOne = in.nextLong();
            long numberTwo = in.nextLong();
            int count=0;
            for(long j=numberOne;j<=numberTwo;j++){
                double numSquareRoot=Math.sqrt(j);
                double numFloor=Math.floor(numSquareRoot);
                if(numSquareRoot == numFloor) count++;

What changes can be made to work efficiently on large numbers?


1 Answer 1


Can be done in \$O(1)\$ time

The count should be:

\$\lfloor{\sqrt n}\rfloor -\lceil{\sqrt m}\rceil + 1\$

or in terms of your program:

return Math.floor(Math.sqrt(numberTwo)) - Math.ceil(Math.sqrt(numberOne)) + 1;
  • \$\begingroup\$ I'm not math background. Mind to explain as simple as you could how you get this? And whats that O(1) time? What topic/subject is that? \$\endgroup\$
    – Coisox
    Jun 3, 2016 at 0:18

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