[C++] 경우의 수

1. 1~n까지 카드를 나열하는 경우의 수
2. 1~n까지 카드 중 중복된 수가 있는 카드를 나열하는 경우 수
1. 1~n까지 카드 중 m개의 카드를 나열하는 경우의 수

- swap 이해 잘하기

#include <iostream>
#include <time.h>
using namespace std;

int arr[7] = { 1,2,3,4,4,6,7 };
int ans[7];
int Cnt = 0;

void recursive(int size) {
	if (size == 7) {
		for (int i = 0; i < 7; i++) {
			cout << ans[i];
		}
		cout << endl;
		Cnt++;
		return;
	}

	for (int i = 0; i < 7; i++) {
		if (arr[i] == 0)
			continue;
		ans[size] = arr[i];
		arr[i] = 0;
		recursive(size+1);
		arr[i] = ans[size];
	}
}

void swap(int index1, int index2) {
	int temp = arr[index1];
	arr[index1] = arr[index2];
	arr[index2] = temp;
}

// swap을 통한 방법
void permutation(int arrSize) {
	if (arrSize == 1) {
		for (int i = 0; i < 7; i++) {
			cout << arr[i];
		}
		cout << endl;
		Cnt++;
		return;
	}

	for (int i = 0; i < arrSize; i++) {
		swap(i, arrSize - 1);
		permutation(arrSize - 1);
		swap(i, arrSize - 1);
	}
}

// 순서가 상관없을 경우
/*void permutation(int index, int arrSize) {
	if (arrSize == 1) {
		for (int i = 0; i < 7; i++) {
			cout << arr[i];
		}
		cout << endl;
		Cnt++;
		return;
	}

	for (int i = index; i < arrSize; i++) {
		swap(i, arrSize - 1);
		permutation(index, arrSize - 1);
		swap(i, arrSize - 1);
	}
}*/

int main() {
	time_t start, end;
	double result;
	start = time(NULL);
	recursive(0);
	//permutation(7); //swap을 이용함
	cout << "count : " << Cnt << endl;
	end = time(NULL);
	result = (double)(end - start);
	cout << result << endl;
	return 0;
}