nPr nCr 기본

1. nPr

#include <iostream>
using namespace std;
int arr[8] = {1,2,3,4,5,6,7,8};
int check[8] = {0};
int su[8];
 
void go(int cnt, int n, int r)
{
    if(cnt == r)
    {
        for(int i = 0 ; i < r ; i++)
            cout << su[i] << ' ';
        cout << '\n';
        return;
    }
 
    for(int i = 0 ; i < n ; i++)
    {
        if(check[i] == 1)
            continue;
        
        su[cnt] = arr[i];
        check[i] = 1;   
        go(cnt+1, n,r);
        check[i] = 0;    // check를 써주고 다시 되돌려주는게 중요.
    }
}
 
int main()  //nPr
{
    int n = 8;
    int r = 3;
 
    
    go(0, 8, 3);
}

2. nCr

#include <iostream>
using namespace std;
int arr[8] = { 1,2,3,4,5,6,7,8 };
int su[8];
 
void go(int su_pos, int arr_pos, long long n, long long r)
{
    if (su_pos == r)
    {
        for (int i = 0; i < r; i++)
        {
            cout << su[i] << " ";
        }
        cout << "\n";
        return;
    }
    if (arr_pos == n)
        return;
 
    su[su_pos] = arr[arr_pos];
    go(su_pos+1, arr_pos+1, n, r);
    go(su_pos, arr_pos+1, n, r);
}
 
 
int main()
{
    go(0, 0, 8, 3);
}