判断一个整数是否满足完美平方？

问题：
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

解决思路：二分查找
java代码如下：

  public boolean isPerfectSquare(int num) {
      if(num < 1) return false;
      long left = 1,right = num;
      while(left<=right) {
          long mid=left+(right-left)/2;
          long t = mid * mid;
          if(t == num){
              return true;
          }else if(t > num){
              right = mid - 1;
          }else{
              left = mid + 1;
          }
      }
      return false;
   }