求n个数的组合的方法

 1 #include <iostream>
 2 #include <fstream>
 3 
 4 using namespace std;
 5 
 6 int main() {
 7     int arr[10];
 8     int n;
 9     int cnt = 0;
10     ofstream fs("a.txt");
11     cin >> n;
12     for(int i = 0; i < n; i++) {
13         cin >> arr[i];
14     }
15     int ss = 1 << n;    //example: n = 4 now ss = (10000)2
16     for(int i = 1; i < ss; i++) {    // i(max) = 1111, means select all numbers of arr.
17         for(int j = 0; j < n; j++) {
18             if(i & (1 << j)) {
19                 cout << arr[j] << " ";
20             }
21         }
22         cnt++;
23         cout << endl;
24     }
25     cout << cnt << endl;
26     return 0;
27 }