367. valid perfect square

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:

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Input: 16
Output: true

Example 2:

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Input: 14
Output: false

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class  {
    public boolean isPerfectSquare(int num) {
        for (int i = 1; num > 0; i += 2) {
            num -= i;
        }
        return 0 == num;
    }
}