Week 1 Kata : String Compression

string_compress.cpp

/*
Problem for week 1: String Compression

Implement a method to perform string compression using counts of repeated characters. String "aabccdaaaaa" becomes "a2b1c2d1a5". The function needs to check for errors and raise an error in case -
1. resultant compressed string is larger 
2. invalid character is found.

The only valid characters fall into [a-zA-Z] range.
*/

#include <iostream>
#include <string>
#include <sstream>
using namespace std;

string compress(const std::string& input)
{
    stringstream resp;
    
    if(input.empty())
        throw "input string empty";
    
    for(auto i = 0 ; i < input.size() ; )
    {
       if(!isalpha(input[i]))
        throw "invalid characters in string";
        
       auto curr_pos = i + 1;
       while((curr_pos < input.size()) && (input[i] == input[curr_pos]))
        ++curr_pos;

       auto rep_cnt = curr_pos - i;
       resp << input[i] << rep_cnt;
       i += (rep_cnt > 1) ? rep_cnt : 1;
    }

      return resp.str();
}

int main()
{
    string input = "aabccdaaaaa";
    try
    {
        auto comp = compress(input);
        if(comp.size() > input.size())
            throw "compressed version longer than input";

        cout<<"Input String is: "<<input<<endl;
        cout<<"Compressed String is: "<<comp<<endl;
    }
    catch(const char* ex)
    {
        cout<<"Error: "<<ex<<endl;
    }
    return 0;
}