combination v1

main.cpp

#include <string>
#include <iostream>
#include <limits>
#include <vector>

using namespace std;

void print_vector(const vector<string>& vector)
{
	for (auto &v: vector)
	{
		std::cout << v << " ";
	}
	std::cout << std::endl;
}

vector<string> element(int x) {
    vector<string> labels;

    for(int i = 0; i < x; i++){
        const string label = get_input<string>("Masukkan nama elemen: ");
        labels.push_back(label);
    }

    return labels;
}

unsigned long long factorial(const unsigned long long n) {
	if (n <= 1) return 1;
	unsigned long long answer = 1;
	
	for(unsigned long long i = 1; i <= n; i++) {
		answer = answer * i;
		//cout << answer << endl;
	}
	
	return answer;
	
}

void enumerate(
    const int n,
    const int r,
    const int start_at,
    vector<string>& labels,
    vector<string>& enumed
)
{
    if (const int temp = static_cast<int>(enumed.size()); temp == r)
    {
		print_vector(enumed);
        return;
    }

    for (int i = start_at; i < n; i++)
    {
        auto current = labels.at(i);
        enumed.push_back(current);
        enumerate(n, r, i+1 ,labels, enumed);
        enumed.pop_back();
    }
}

unsigned long long get_combination(const int n, const int r)
{
	if (n == r) return 1;

	unsigned long long hasil = 0;
	// n/r!
	for (int i = n; i > r; i--) {
		hasil = hasil * i;
	}

	hasil = hasil / factorial(n - r);
	return hasil;
}

/**
 * prompts user with y/n question
 * returns true if user answers with y 
 * */
bool confirm(const string &prompt) {
	bool is_valid = false;
	bool wants_to_repeat = false;
	char answer;
	
	do {
		cout << prompt;
		cin >> answer;
		
		if (answer != 'n' && answer != 'y') {
			cout << "invalid." << endl;
			continue;
		}
		
		wants_to_repeat = answer == 'y';
		is_valid = true;
	} while (!is_valid);
	
	return wants_to_repeat;
}

template <typename T>
T get_input(const string prompt, const string &invalid_message = "invalid input.")
{
	bool is_valid = false;
	T input;

	while (!is_valid)
	{
		cout << prompt;
		cin >> input;

		if(!cin) {
			cin.clear();
			cin.ignore(numeric_limits<streamsize>::max(), '\n');
			cout << invalid_message << endl;
			continue;
		}

		is_valid = true;
	}

	return input;
}

int main ()
{
	bool wants_to_repeat = false;
	
	cout << "=====kalkulator kombinatorial tanpa pengulangan=====\n";

	int n = 0,
		r = 0;
	do {
		bool repeat_input_numbers = true;

		do {
			n = get_input<int>("masukkan jumlah seluruh elemen :");
			r = get_input<int>("masukkan elemen yang ingin dipilih :");

			if (r > n) {
				cout << "Tidak valid. n harus lebih besar dari r" << endl;
				continue;
			}
			
			cout << "C(" << n << "," << r << ")" << endl;
			// if user answers no, repeat
			repeat_input_numbers = !confirm("apakah angka diatas benar (y/n) :");
			
			if(repeat_input_numbers) {
				cout << "silahkan mengulang.\n\n";
			}
			
		} while (repeat_input_numbers);
		
		cout << "\n======================================";
		cout << "\n|             Menu Utama             |";
		cout << "\n======================================\n";
		cout << "1. hanya rumus.\n";
		cout << "2. hanya enumerasi.\n";
		cout << "3. dengan rumus dan enumerasi.\n";

		int pilih_menu = get_input<int>("pilih menu: ");

		switch (pilih_menu) {
			case 1 : {
				unsigned long long hasil = get_combination(n, r);
				vector<string> enumed;

				cout << "=====hanya menggunakan rumus=====\n";
				cout << n << "! / " << r << "!" << "(" << n << "-" << r << ")!" << endl;

				cout << hasil << endl;
				wants_to_repeat = confirm("apakah anda ingin kembali ke menu utama? (y/n): ");

				break;
			}
			case 2 : {
				vector<string> labels = element(n);
				vector<string> enumed;
				
				enumerate(n, r, 0, labels, enumed);
				
				wants_to_repeat = confirm("apakah anda ingin kembali ke menu utama? (y/n): ");
				
				labels.clear();
				enumed.clear();
				
				break;
			}
			case 3 : {
				unsigned long long hasil = get_combination(n, r);
				vector<string> labels = element(n);
				vector<string> enumed;

				cout << "===== Menggunakan rumus dan enumerasi =====\n";
				cout << n << "! / " << r << "!" << "(" << n << "-" << r << ")!" << endl;
				cout << hasil << endl;
				
				enumerate(n, r, 0, labels, enumed);
				
				wants_to_repeat = confirm("apakah anda ingin kembali ke menu utama? (y/n): ");
				cout << endl;

				break;
			}
			default: {
				cout << "tolong masukkan input yang valid (1-3)." << endl;
			}
		}
	} while (wants_to_repeat);

	return 0;
}

vector<string> element(int x) {
    vector<string> labels;

    for(int i = 0; i < x; i++){
        const string label = get_input<string>("Masukkan nama elemen: ");
        labels.push_back(label);
    }

    return labels;
}

input elemen