VC++

#include <iostream>
#include <fstream>
#include <map>
#include <vector>
#include <string>
#include <sstream>

using namespace std;

map<string, double> gerrymanderingRatios(const string &file);
void printMap(map<string, double>);

int main() {
    cout << "output should be something like: {\"D\":1.3, \"R\":0.742857}" << endl;
    printMap(gerrymanderingRatios("data.txt"));
    cout << endl;
    system("pause");
    return EXIT_SUCCESS;
}

void printMap(map<string, double> in) {
    map<string, double>::iterator dit;
    for (pair<string, double> p : in) {
      cout << '{' << p.first << ":" << p.second << "} ";
    }
}

map<string, double> gerrymanderingRatios(const string &file) {
    //countMap<string, int> {D:14, R:13}
    map<string, int> countMap;          // party : votes

    //districtWinner <string, string>{1:D, 2:R, 2:R, 4:D, 5:D}
    map<string, string> districtWinner; // district : winning party

    vector<string> districtVotes;       // temp storage for each district's votes

    map<string, double> gerryMap;       // party : ratio (return)
    ifstream file_in(file, ios::in);
    double totalVotes = 0.0;
    double districtCounter = 0.0;
    if (file_in) {
        string line, districtName, partyVote, majorityVote;
        while (file_in >> districtName, getline(file_in, line)) {
            stringstream ss(line);
            while (ss >> partyVote) {
                try {
                    ++countMap[partyVote];
                } catch (const out_of_range& oor) {     // if key not present,
                    countMap[partyVote] = 1;            // adds and begin counting
                }
                districtVotes.push_back(partyVote);
                ++totalVotes;
            }
            // iterate over districtVotes, insert majority party into districtWinner
            for (size_t i = 0; i < districtVotes.size() - 1; ++i) {
                string winner = districtVotes[i];
                int counter = 0;
                int maxCounter = 0;
                if (districtVotes[i + 1] == districtVotes[i]) {
                    winner = districtVotes[i + 1];
                    ++counter;
                }
                else {
                    if (counter > maxCounter)
                        counter = maxCounter;
                    majorityVote = districtVotes[maxCounter];
                    counter = 0;
                }
                districtWinner[districtName] = majorityVote;
            }
            districtVotes.clear();
            ++districtCounter;
        }
    }
    file_in.close();

    map<string, int>::iterator voteCounter = countMap.begin(); // countMap
    for (; voteCounter != countMap.end(); ++voteCounter) {
        map<string, string>::iterator partyCounter = districtWinner.begin(); // districtWinner
        int districtsWon = 0;
        for (; partyCounter != districtWinner.end(); ++partyCounter) {
            if ((*voteCounter).first == (*partyCounter).second)
                ++districtsWon;
        }
        double percentOfVotes = (*voteCounter).second / totalVotes; // total votes / # of party votes
        double percentDistrictsWon = districtsWon / districtCounter; // districts won by party / # of districts
        double ratio = percentDistrictsWon / percentOfVotes;
        gerryMap[(*voteCounter).first] = ratio;
    }
    return gerryMap;
}