Outputs all non-empty combinations for given number. `assert(n > 0)`

Combinations.cpp

#include <iostream>
#include <vector>
#include <numeric>

bool lift(std::vector<int>& vec, int limit) {
	if (vec.back() < limit) {
		vec.back() += 1;
		return true;
	}
	for (auto rit = std::next(vec.rbegin()); rit != vec.rend(); rit++) {
		if (*rit + 1 < *std::prev(rit)) {
			*rit += 1;
			return true;
		}
	}
	return false;
}

int main() {
	int n;
	std::cin >> n;
	for (int k = 1; k < n + 1; ++k) {
		std::vector<int> vec(k);
		std::iota(vec.begin(), vec.end(), 1);
		do {
			std::cout << k;
			for (auto el: vec) {
				std::cout << " " << el;
			}
			std::cout << std::endl;
		} while (lift(vec, n));
	}
	return 0;
}