class Solution {
 public:
     bool isPerfectSquare(int num) {
         if(num == 1){return true;}
         int low = 1;
         int high = num / 2;
         while(low <= high){
             long mid = (low + high) / 2;
             if(mid * mid == num){return true;}
             else if(mid * mid < num){
                 low = mid + 1;
             }
             else if(mid * mid > num){
                 high = mid - 1;
             }
         }
         return false;
     }
 };

367. Valid Perfect Square

Easy

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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