[leetcode]367. Valid Perfect Square验证完全平方数

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

 

题意：

验证完全平方数

 

思路：

二分查找，可回顾之前[leetcode]278. First Bad Version首个坏版本 笔记

需要注意的是类型声明为long

 

代码：

class Solution {
  public boolean isPerfectSquare(int num) {
        long left = 0;
        long right = num;

        while (left <= right) {
            long mid = left + (right - left) / 2;
            if (mid * mid == num) {
                return true;
            } else if (mid * mid < num) {
                left = mid + 1;
            } else {
                right = mid - 1;
            }
        }
        return false;
    }    
}