AbsolutePermutation.cpp

#include <bits/stdc++.h>

using namespace std;

string ltrim(const string &);
string rtrim(const string &);
vector<string> split(const string &);

/*
 * Complete the 'absolutePermutation' function below.
 *
 * The function is expected to return an INTEGER_ARRAY.
 * The function accepts following parameters:
 *  1. INTEGER n
 *  2. INTEGER k
 */

vector<int> absolutePermutation(int n, int k) {
    // Case when k is 0, return the identity permutation
    if (k == 0) {
        vector<int> permutation(n);
        iota(permutation.begin(), permutation.end(), 1);
        return permutation;
    }

    // If n is not divisible by 2 * k, a valid permutation is not possible
    if (n % (2 * k) != 0)
        return {-1};

    vector<int> permutation;
    bool add = true;

    // Iterate through numbers and alternate between adding and subtracting k
    for (int i = 1; i <= n; ++i) {
        if (add) {
            permutation.push_back(i + k);
        } else {
            permutation.push_back(i - k);
        }

        // Flip `add` every k steps
        if (i % k == 0) {
            add = !add;
        }
    }

    return permutation;
}

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

    string t_temp;
    getline(cin, t_temp);

    int t = stoi(ltrim(rtrim(t_temp)));

    for (int t_itr = 0; t_itr < t; t_itr++) {
        string first_multiple_input_temp;
        getline(cin, first_multiple_input_temp);

        vector<string> first_multiple_input = split(rtrim(first_multiple_input_temp));

        int n = stoi(first_multiple_input[0]);

        int k = stoi(first_multiple_input[1]);

        vector<int> result = absolutePermutation(n, k);

        for (size_t i = 0; i < result.size(); i++) {
            fout << result[i];

            if (i != result.size() - 1) {
                fout << " ";
            }
        }

        fout << "\n";
    }

    fout.close();

    return 0;
}

string ltrim(const string &str) {
    string s(str);

    s.erase(
            s.begin(),
            find_if(s.begin(), s.end(), not1(ptr_fun<int, int>(isspace)))
    );

    return s;
}

string rtrim(const string &str) {
    string s(str);

    s.erase(
            find_if(s.rbegin(), s.rend(), not1(ptr_fun<int, int>(isspace))).base(),
            s.end()
    );

    return s;
}

vector<string> split(const string &str) {
    vector<string> tokens;

    string::size_type start = 0;
    string::size_type end = 0;

    while ((end = str.find(" ", start)) != string::npos) {
        tokens.push_back(str.substr(start, end - start));

        start = end + 1;
    }

    tokens.push_back(str.substr(start));

    return tokens;
}