Check perfect square using addition/subtraction

Property: Sum of all consecutive odd number always a perfect square.

Proof:

1 + 3 + 5 + ...  (2n-1) = n/2*[ 1+ (2n-1)] = n/2*[2n]

                        = n^2

Sum of A.P. = terms/2*{first_term+last_term}

Using this property, we can write the pseudo code:

boolean  perfectSqr(int num) {

       int sum = 0;

       for(int i=1; sum<num; i+=2) {

                    sum += i;

                    if (sum == num)

                             return true;

                             break;

                    }

       }
       return false;

}