[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;
     }
 }