（一）增量构造法

#include <iostream>
#include <algorithm>
using namespace std;

const int MAXN = 1000;
int A[MAXN], n;

void print_subset(int n, int *A, int cur) {
	for(int i = 0; i < cur; ++i) cout << A[i] << " ";
	cout << endl;
	int s = (cur ? A[cur-1]+1 : 0);    //选取当前填到第cur个位置上的可以填的最小是数字！
	for(int i = s; i < n; ++i) {
		A[cur] = i;
		print_subset(n, A, cur+1);
	}
}

int main() {
	cin >> n;
	print_subset(n, A, 0);
	return 0;
}

#include <iostream>
#include <algorithm>
using namespace std;

const int MAXN = 1000;
int B[MAXN], n;

void print_subset(int n, int *B, int cur) {
	if(cur == n) {
		for(int i = 0; i < cur; ++i) {
			if(B[i]) cout << i << " ";
		}
		cout << endl;
		return ;
	}
	B[cur] = 1;                 //选第cur个元素
	print_subset(n, B, cur+1);
	B[cur] = 0;                 //不选第cur个元素
	print_subset(n, B, cur+1);
}

int main() {
	cin >> n;
	print_subset(n, B, 0);
	return 0;
}