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  1. #include <iostream>
  2. #include <map> 
  3. #include <vector>
  4. using namespace std;
  5.  
  6. vector<vector<int>> fun(int pos, int n, int k, vector<int> &a) {
  7. 	if (pos == n || k == 0) {
  8. 		return {};
  9. 	}
  10. 	vector<vector<int>> ret;
  11. 	//include current element("pos") to the combinations
  12. 	auto v = fun(pos + 1, n, k - 1, a);
  13. 	for (auto c: v) {
  14. 			vector<int> cur = {a[pos]};
  15. 			//appends vector c to cur
  16. 			cur.insert(cur.end(), c.begin(), c.end());
  17. 			ret.push_back(cur);
  18. 	}
  19. 	if (k == 1) {
  20. 		ret.push_back({a[pos]});
  21. 	}
  22. 	//exclude current element("pos") from the combinations
  23. 	auto f = fun(pos + 1, n, k, a);
  24. 	//appends all vectors returned by f to the current result
  25. 	ret.insert(ret.end(), f.begin(), f.end());
  26. 	return ret;
  27. }
  28.  
  29. int main() {
  30. 	vector<int> a = {1, 2, 3, 4, 5};
  31. 	int n = a.size(), k = 3;
  32. 	auto res = fun(0, n, k, a);
  33. 	for (auto v: res) {
  34. 		for (auto x: v) {
  35. 			cout << x << " ";
  36. 		} 
  37. 		cout << "\n";
  38. 	}
  39. 	cout << "Total number of " << k << "-combinations of " << n << "-elements set: " << res.size() << endl;
  40. 	return 0;
  41. }
Success #stdin #stdout 0.01s 5316KB
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Standard input is empty
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1 2 3 
1 2 4 
1 2 5 
1 3 4 
1 3 5 
1 4 5 
2 3 4 
2 3 5 
2 4 5 
3 4 5 
Total number of 3-combinations of 5-elements set: 10
https://ideone.com/9WNddC
language:
C++14 (clang 8.0)
created:
2 years ago
visibility:
public

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