sort Char By Frequency Algorithm
However, although optimal among methods encode symbols separately, Huffman coding is not always optimal among all compression methods-it is replaced with arithmetical coding or asymmetrical numeral systems if better compression ratio is need. In computer science and information theory, a Huffman code is a particular type of optimal prefix code that is normally used for lossless data compression. In making so, Huffman outdid Fano, who had worked with information theory inventor Claude Shannon to develop a like code. The professor, Robert M. Fano, assigned a term paper on the problem of finding the most efficient binary code. In 1951, David A. Huffman and his MIT information theory classmates were given the choice of a term paper or a final exam.
/*
* Given a string, sort it in decreasing order based on the frequency of characters.
* Example:
* Input: cccbbbbaa
* Output: bbbcccaa
*
* Input: AaaBBaa
* Output: aaaaBBA
*
* Input: cccaaa
* Output:cccaaa or aaaccc
*
* Notice that order of chars in alphabatical order does not matter for same frequency elements.
* However, also all the same characters should be together. cacaca will not be a valid answer.
*/
#include <iostream>
#include <unordered_map>
#include <map>
std::string frequencySort(std::string s) {
// Create a hash map of our characters with frequency as their values.
std::unordered_map<char,int> frequencyMap;
for (char c : s) {
frequencyMap[c]++;
}
// Now we will maintain an another ordered map whose key would be
// the frequency and values would be accumulated chars of same frequency.
//
std::map<int, std::string> stringMap;
for (auto frqPair : frequencyMap) {
char c = frqPair.first;
int n = frqPair.second;
stringMap[n] += std::string(n, c);
}
// Now pick the accumulated string in reverse order (highest first)
std::string result;
for (auto it = stringMap.rbegin(); it != stringMap.rend(); ++it) {
result += it->second;
}
return result;
}
int main()
{
std::string input1{"cccbbbbaa"};
std::cout << "Input: " << input1 << std::endl;
std::cout << "Output:" << frequencySort(input1) << std::endl;
std::string input2{"cccaaa"};
std::cout << "Input:" << input2 << std::endl;
std::cout << "Output:" << frequencySort(input2) << std::endl;
return 0;
}
