Valid Perfect Square

Description

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

code

class Solution {
    public boolean isPerfectSquare(int num) {
        int lo = 1, hi = num;
        while (lo < hi) {
            int mid = lo - (lo - hi) / 2;
            long temp = (long) mid * mid;
            if (temp == num) return true;
            else if (temp < num) lo = mid + 1;
            else hi = mid - 1;
        }
        return lo * lo == num;
    }
}