title: Maximum number that can be formed from the given digits
body: <p>Given a Integer, find the maximum number that can be formed from the digits. 
  Input : 8754365 
  output : 8765543 </p>
  
  <p>I told solution in $O(n logn)$. He asked me optimize further.</p>
  
  <p>We can use Hash Table to optimize further, $\rightarrow$ O(n)</p>
  
  <p>Algorithm:
  1. Take a hash table with size 10 (0 to 9).
  2. Store the count of every digit from 0 to 9.
  3. Print the index of the Hash table with respect to digit count in the reverse direction (from 9 to 0).</p>
  
  <p>Example: </p>
  
  <p>Hash table after digit count for 8754365 $\rightarrow$ (0 0 0 1 1 2 1 1 1 0) 
  Print the index of the hash table with respect to their count in reverse order $\rightarrow$ 8765543
  Time Complexity : O(n)
  Correct me if I am wrong.</p>