Sort a string of Roman Numerals

Question

The input will be a string of Roman numerals that have to be sorted by their value. Also this task has to be completed using classes in c++

So far I've created my class

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

class RomanNumbers
{
public:
    RomanNumbers(string = "");

    void setRoman(string);

    int convertToDecimal();

    void printDecimal();

    void printRoman();


private:

    string roman;

    int decimal;

};

And the functions to convert a number from Roman numeral to integer form but my question is : How shall I sort them because I can't create a new string that will contain the converted Roman numerals and sort the string. Any help will be appreciated.

#include<iostream>
#include<string>
#include "RomanNumbers.h"
using namespace std;

RomanNumbers::RomanNumbers(string myRoman)
{
    roman = myRoman;
    decimal = 0;
}

void RomanNumbers::setRoman(string myRoman)
{
    roman = myRoman;
    decimal = 0;
}

int RomanNumbers::convertToDecimal()
{
    enum romans { I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000 };

    for (int i = 0; i < roman.size(); i++)
    {
        switch (roman[i])
        {

         case 'M': decimal += M; break;
         case 'D': decimal += D; break;
         case 'C': decimal += C; break;
         case 'L': decimal += L; break;
         case 'X': decimal += X; break;
         case 'V': decimal += V; break;

         case 'I':
             if (roman[i + 1] != 'I' && i + 1 != roman.size())
             {
                 decimal -= 1;
             }
             else
             {
                 decimal += 1;
             }
               break;

        }
    }

    return decimal;
}

void RomanNumbers::printRoman()
{
    cout << "Number in Roman form : " << roman;
    cout << endl;
}

void RomanNumbers::printDecimal()
{
    cout << "Number converted in integer form : " << decimal;

    cout << endl;
}

You can create a new array/vector of your values stored as std::pair<int,std::string> and sort that, or you can make a custom sorting predicate passed to std::sort that uses your conversion function to compare values. — paddy
Also notice that your conversion will not work for numbers like XC (90) — DannyPhantom
I'm not sure what you mean by “sort the string”. Don't you want to sort by the number? Unless you're doing an alphabetical sort (C, CC, CCC, CCCI, CCCII, CCCIII, CCCIV, CCCIX, CCCL, CCCLI, etc.). — dan04
@Triple3XH: Plenty of existing questions on that here on StackOverflow. Check for "operator overloading". — MSalters

Ziezi Ziezi · Accepted Answer · 2017-03-27T22:39:27

One way to tackle your problem is through a definition of a meaningful comparison operator< / comparison lambda expression / comparison class, which then be used along with the sort algorithm:

template <class RandomAccessIterator, class Compare>
void sort (RandomAccessIterator first, RandomAccessIterator last, Compare comp);

for example a comparison class would be:

struct RomanComp 
{
    bool operator() const (const RomanNumbers& lhs, const RomanNumbers& rhs)
    { 
        return lhs.decimal < rhs.decimal;
    }
} RomanComparator; // <--- note object instantiation

and then to sort a vector of roman number for example, you do:

std::vector<RomanNumbers> nums;

std::sort(nums.begin(), nums.end(), RomanComparator);

assuming:

#include <algorithm>    // std::sort
#include <vector>       // std::vector

Sort a string of Roman Numerals

1 Answers