need help on c++ small project

A encode and decode functions based on huffman coding. What I need: Encoder.h & Encoder.cpp, which have:
//public constructor passing array of letter frequencies.
Encoder(std::shared_ptr<std::vector<int>>);

//Encode std::string into a sequence of bytes.
std::shared_ptr<std::vector<char>> Encode(std::string);

//Decode an array of bytes into a std::string.
std::string Decode(std::shared_ptr<std::vector<char>>);