[leetcode]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:
*
* Input: 16
* Returns: True
* Example 2:
*
* Input: 14
* Returns: False
****************************************************************************/

/* 1 最容易想到的 */
class Solution {
    public boolean isPerfectSquare(int num) {
        if (Math.ceil(Math.sqrt(num)) * Math.ceil(Math.sqrt(num)) == num) return true;
        else return false;
    }
}

牛頓法 原理：

/* Newton's method */
public boolean isPerfectSquare(int num) {
        long x = num;
        while (x * x > num) {
            x = (x + num / x) >> 1;
        }
        return x * x == num;
    }