#include <iostream>
#include <list>
#include <algorithm>
#include <numeric>
#include <fstream>
#include <sstream>
#include <iterator>
#include <string>
#include <experimental/filesystem>

namespace fs = std::experimental::filesystem;

uint64_t calc_answer(const std::list<int>& list)
{
    int left_sum = 0;
    int right_sum = std::accumulate(list.begin(), list.end(), 0);

    uint64_t index_sum = 0;
    int curr_index = 0;

    std::for_each(list.begin(), list.end(), [&] (int val) {
        right_sum -= val;

        if(left_sum == right_sum)
            index_sum += curr_index;

        left_sum += val;

        ++curr_index;
    });

    return index_sum;
}

std::string read_file(const fs::path& file_path)
{
    if(!fs::exists(file_path))
        return "";

    std::ifstream infile{file_path.string()};

    std::string data{""};

    std::string row{""};
    while(std::getline(infile, row))
        data.append(row);

    return data;
}

struct Facet : std::ctype<char>
{
    using ParentT = std::ctype<char>;

    Facet(std::size_t refs = 0) : ParentT(make_table(), false, refs) {}

    static const mask* make_table()
    {
        static mask char_table[table_size];
        static int fake = (std::copy(classic_table(), classic_table() + table_size, char_table),
                           (void)fake, 0);

        char_table[','] |= space;

        return char_table;
    }
};

std::list<int> parse_raw_data(const std::string& raw_data)
{
    std::istringstream iss{raw_data};
    iss.imbue(std::locale{iss.getloc(), new Facet{}});

    std::list<int> data{};

    using ISIt = std::istream_iterator<int>;
    std::copy(ISIt{iss}, ISIt{}, std::back_inserter(data));

    return data;
}

int main()
{
    const fs::path DATA_PATH{"data.txt"};

    std::string raw_data = read_file(DATA_PATH);

    if(raw_data.empty())
    {
        std::cout << "File 'data.txt' not found or empty. Terminate..." << std::endl;
        return 0;
    }

    std::list<int> data = parse_raw_data(raw_data);

    std::cout << "Sum of indexes that satisfies specified propery: " << calc_answer(data) << std::endl;

    return 0;
}

#include <iostream>
#include <list>
#include <algorithm>
#include <numeric>
#include <fstream>
#include <sstream>
#include <iterator>
#include <string>
#include <experimental/filesystem>

namespace fs = std::experimental::filesystem;

uint64_t calc_answer(const std::list<int>& list)
{
    int left_sum = 0;
    int right_sum = std::accumulate(list.begin(), list.end(), 0);

    uint64_t index_sum = 0;
    int curr_index = 0;

    std::for_each(list.begin(), list.end(), [&] (int val) {
        right_sum -= val;

        if(left_sum == right_sum)
            index_sum += curr_index;

        left_sum += val;

        ++curr_index;
    });

    return index_sum;
}

std::list<int> read_file(const fs::path& file_path)
{
    if(!fs::exists(file_path))
        return std::list<int>{};

    std::ifstream infile{file_path.string()};

    std::list<int> data{};

    std::string number{""};
    while(std::getline(infile, number, ','))
        data.push_back(std::stoi(number));

    return data;
}

int main()
{
    const fs::path DATA_PATH{"data.txt"};

    std::list<int> data = read_file(DATA_PATH);

    if(data.empty())
    {
        std::cout << "File 'data.txt' not found or empty. Terminate..." << std::endl;
        return 0;
    }

    std::cout << "Sum of indexes that satisfies specified propery: "
              << calc_answer(data) << std::endl;

    return 0;
}