Valid Perfect Square

Introduction Link to heading

Given a positive integer num, write a function which returns True if num is a perfect square else False.

Note: Do not use any built-in library function such as sqrt.

Example 1:

Input: 16
Output: true

Example 2:

Input: 14
Output: false

Solution Link to heading

Let’s use the binary search to find the solution.

func isPerfectSquare(num int) bool {
    lo, hi := 1, num
    for lo < hi {
        mi := (hi - lo) >> 1 + lo
        val := mi * mi
        if val == num {
            return true
        } else if val > num {
            hi = mi
        } else {
            lo = mi + 1
        }
    }
    return lo * lo == num
}