从unordered_set获取给定大小k的所有子集？

#include <iostream>
#include <unordered_set>
#include <vector>

using namespace std;

void backtrack(unordered_set<int>& nums, vector<int>& temp, vector<vector<int>>& res, int start, int k) {
    if (temp.size() == k) {
        res.push_back(temp);
        return;
    }
    
    for (int i = start; i < nums.size(); i++) {
        temp.push_back(nums[i]);
        backtrack(nums, temp, res, i + 1, k);
        temp.pop_back();
    }
}

vector<vector<int>> getSubsets(unordered_set<int>& nums, int k) {
    vector<vector<int>> res;
    vector<int> temp;
    backtrack(nums, temp, res, 0, k);
    return res;
}

int main() {
    unordered_set<int> nums = {1, 2, 3, 4};
    int k = 2;
    vector<vector<int>> subsets = getSubsets(nums, k);
    
    for (const auto& subset : subsets) {
        for (const auto& num : subset) {
            cout << num << " ";
        }
        cout << endl;
    }
    
    return 0;
}