LeetCode "Valid Perfect Square"

class Solution {
public:
bool isPerfectSquare(int num) {
if(num < 0) return false;
if(num < 2) return true;

long long i = 1, j = num - 1;
while(i <= j)
{
long long mid = (i + j) / 2;
long long r = mid * mid;

if(r == num) return true;
if(r < num) i = mid + 1;
else j = mid - 1;
}
return false;
}
};