12787 - Base64 Encoding   

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Description

In computer science, Base64 is a binary-to-text encoding method. Here is how Base64 encoding works.
Given a string that contains ASCII characters:

  1. First, you need to turn each character to its ASCII number then to its 8-bits binary number,
  2. Second, connect all the binary numbers, from the first binary, and replace every 6 bits by its corresponding Base64 character, where such mapping is provided in the Base64 index table below.
  3. Last, if the total length of all the binary numbers (in terms of bits) is not a multiple of 6, add zero until the total length is a multiple of 6, and for every 2 zero you add, add a '=' character to your encoded string.

ouo.

The ASCII code table is as follows:

 

The Base64 index table is as follows: (From WIKI)

Sample Input 1:
Turn the string "Man" to ASCII numbers:
M = 77, a = 97, n = 110.

Turn ASCII numbers to 8-bits binary numbers:
77 = 01001101, 97 = 01100001, 110 = 01101110,
010011 / 010110 / 000101 / 101110

Replace every 6 bits by the corresponding character as the table above:
010011 = T / 010110 = W / 000101 = F / 101110 = u

Base64 encoding of "Man" is "TWFu"

Sample Input 2:
Turn the string "Ma" to ASCII numbers:
M = 77, a = 97.

Turn ASCII numbers to 8-bits binary numbers:
77 = 01001101, 97 = 01100001.
010011 / 010110 / 0001

The length is not a multiple of 6, add zero until it becomes a multiple of 6. So we add 2 zero:
010011 / 010110 / 000100

Replace every 6 bits by the corresponding character as the table above:
010011 = T / 010110 = W / 000100 = E

For every 2 zero you add, add 1 '=' to the Base64 encoding result. So we add 1 '=':
Base64 encoding of "Ma" is "TWE="

Sample Input 3:
Turn the string "M" to ASCII numbers:
M = 77.

Turn ASCII numbers to 8-bits binary numbers:
77 = 01001101.
010011 / 01

The length is not a multiple of 6, add zero until it becomes a multiple of 6. So we add 4 zero:
010011 / 010000

Replace every 6 bits by the corresponding character as the table above:
010011 = T / 010000 = Q

For every 2 zero you add, add 1 '=' to the Base64 encoding result. So we add 2 '=':
Base64 encoding of "M" is "TQ=="

The class inheritance hierarchy of this problem is given below:

class Codec {
protected:
  bool encoded;
  string code_str;
public:
  Codec(string& code_str): code_str(code_str), encoded(false) {}
  virtual void encode() = 0;
  virtual void decode() = 0;
  virtual void print(ostream& os) const = 0;
  virtual bool is_encoded() const = 0;
};

class Base64Codec: public Codec {
private:
  // Given 6-bits binary number, return with the Base64 encode character
  char encodeCharacter(int binaryNumber) const;
public:
  // Inherit from base class
  Base64Codec(string& code_str): Codec(code_str) {}
  // TODO: Encode the code_str
  void encode() override;
  // Decode the code_str
  void decode() override;
  // Print the code_str
  void print(ostream& os) const override;
  // Get code_str status
  bool is_encoded() const override;
};

 

In this problem, you only need to implement the member function encode() of class Base64Codec.

Note:

1.  We have implemented the encodeCharacter(int binaryNumber) function in class Base64Codec for you, whose details are further explained below:

Given a binaryNumber in decimal, representing a 6-bits binary number, encodeCharacter() returns the corresponding character to Base64 encoding.

Example:
binaryNumber = 19(decimal) = 010011(binary),
encodeCharacter(binaryNumber) returns character 'T'

2. You should choose 'C++11' on submission.

Input

The input contains 1 line: a string S.

The string will only contain characters A~Z, a~z, 0~9, space, comma(',') and period('.')

It is guaranteed that:
1 <= |S| <= 2000

Output

The output contains only 1 line: the Base64 encoding of the given string.

With a new line character after your output.

Sample Input  Download

Sample Output  Download

Partial Judge Code

12787.cpp

Partial Judge Header

12787.h

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