sock_merchant.cpp

#include <bits/stdc++.h>
#include <unordered_set>

using namespace std;

vector<string> split_string(string);



/////////////////// SOLUTION //////////////////////////
/**
  * @brief Count the pairs using recursion 
  */
int count_pairs( const vector<int>& in_ar, const unsigned int i, unordered_set<int>& arr_unp, const unsigned int pairs )
{
    if(i<in_ar.size())
    {
        auto temp = arr_unp.find(in_ar[i]); 
        if(temp == arr_unp.end()) {arr_unp.insert(in_ar[i]); return count_pairs(in_ar, i+1, arr_unp, pairs);}  
        else if(temp != arr_unp.end()) { arr_unp.erase(temp); return count_pairs(in_ar, i+1, arr_unp, pairs+1); } 
    } 
    return pairs; 
}

// Complete the sockMerchant function below.
int sockMerchant(int n, vector<int> ar) 
{
    unordered_set<int> temp; 
    return count_pairs(ar, 0, temp, 0); 
}

///////////////////////////////////////////////////////

int main()
{
    ofstream fout(getenv("OUTPUT_PATH"));

    int n;
    cin >> n;
    cin.ignore(numeric_limits<streamsize>::max(), '\n');

    string ar_temp_temp;
    getline(cin, ar_temp_temp);

    vector<string> ar_temp = split_string(ar_temp_temp);

    vector<int> ar(n);

    for (int i = 0; i < n; i++) {
        int ar_item = stoi(ar_temp[i]);

        ar[i] = ar_item;
    }

    int result = sockMerchant(n, ar);

    fout << result << "\n";

    fout.close();

    return 0;
}

vector<string> split_string(string input_string) {
    string::iterator new_end = unique(input_string.begin(), input_string.end(), [] (const char &x, const char &y) {
        return x == y and x == ' ';
    });

    input_string.erase(new_end, input_string.end());

    while (input_string[input_string.length() - 1] == ' ') {
        input_string.pop_back();
    }

    vector<string> splits;
    char delimiter = ' ';

    size_t i = 0;
    size_t pos = input_string.find(delimiter);

    while (pos != string::npos) {
        splits.push_back(input_string.substr(i, pos - i));

        i = pos + 1;
        pos = input_string.find(delimiter, i);
    }

    splits.push_back(input_string.substr(i, min(pos, input_string.length()) - i + 1));

    return splits;
}