Given a string S, implement Huffman Encoding and Decoding.

Example 1:

Input : abc
Output : abc

Example 2: 

Input : geeksforgeeks
Output : geeksforgeeks

Your task: 
You don't need to read input or print anything. Your task is to complete the function decode_file(), which takes root of the tree formed while encoding and the encoded string as the input parameters and returns the decoded string.

Constraints:
2<=S<=1000