Check if a number is a perfect square?

public bool IsPerfectSquare(int num) {

if (num < 0) return false;

int left = 0, right = num;

while (left <= right) {

int mid = left + (right - left) / 2;

long sq = (long)mid * mid;

if (sq == num) return true;

else if (sq < num) left = mid + 1;

else right = mid - 1;

return false;

Explanation:

Binary search for integer square root and check if square equals num.