TopCoder SRM 582 DIV2 250

Problem Statement
	Magical Girl Iris loves perfect squares. A positive integer n is a perfect square if and only if there is a positive integer b >= 1 such that b*b = n. For example, 1 (=1*1), 16 (=4*4), and 169 (=13*13) are perfect squares, while 2, 54, and 48 are not. Iris also likes semi-squares. A positive integer n is called a semi-square if and only if there are positive integers a >= 1 and b > 1 such that a < b and a*b*b = n. For example, 81 (=1*9*9) and 48 (=3*4*4) are semi-squares, while 24, 63, and 125 are not. (Note that we require that a < b. Even though 24 can be written as 6*2*2, that does not make it a semi-square.) You are given a int N. Return "Yes" (quotes for clarity) if N is a semi-square number. Otherwise, return "No".
Definition
	Class: SemiPerfectSquare Method: check Parameters: int Returns: string Method signature: string check(int N) (be sure your method is public)
Notes
-	The return value is case-sensitive. Make sure that you return the exact strings "Yes" and "No".
Constraints
-	N will be between 2 and 1000, inclusive.
Examples
0)
	48 Returns: "Yes" 48 can be expressed as 3 * 4 * 4. Therefore, 48 is a semi-square.
1)
	1000 Returns: "No" 1000 can be represented as 10 * 10 * 10, but it doesn't match the definition of semi-perfect squares.
2)
	25 Returns: "Yes"
3)
	47 Returns: "No"
4)
	847 Returns: "Yes"

Code:

#include
#include
using namespace std;

class SemiPerfectSquare
{
public:
	string check(int n){
		int i,j,mul;
		string str="No";
		for(i=2;i*i<=n;i++){
			mul=i*i;
			for(j=1;j