Valid Perfect Square - The Equation

You need to find if there exists an integer $k$ such that $k^2 = num$. This is a quadratic equation.

One approach: compute $\sqrt{num}$ and check if it's an integer. But floating point can be imprecise.

Better approach: use binary search to find $k$ in the range $[1, num]$. If $k^2 = num$ exactly, return true.