title: how to two binary strings, return their sum (also a binary string)
body: <p>Example:</p>
  
  <p>a = "100"</p>
  
  <p>b = "11"</p>
  
  <p>Return a + b = “111”.</p>
  
  <p>its done by parsing int but when two strings are more then int size then it will not working.</p>
  
  <p>i tried with long :</p>
  
  <pre><code>long a1=Long.parseLong(a,2);
  long b1=Long.parseLong(b,2);
  long sum=a1+b1;
  String ans=Long.toBinaryString(sum);
  </code></pre>
  
  <p>is there any methods for double?? </p>