从n个元素中,抽出r个元素(其中n个元素为自然数1,2,3,...,n)
#include <iostream>
#include <algorithm>
#include <iomanip>
using namespace std;
#define maxn 30
int num[maxn];
int main() {
int n, r;
cin >> n >> r;
for (int i = r + 1; i <= n; i++) {
num[i] = 1;
}
do {
for (int i = 1; i <= n; i++) {
if (!num[i])
cout << setw(3) << i;
}
cout << endl;
} while (next_permutation(num + 1, num + 1 + n));
return 0;
}