Leetcode #78: Subsets

Leetcode_78.cpp

class Solution {
    vector<vector<int>> answer;
    vector<int> numbers;
    
    void recurse(vector<int> path, int startIndex) {
        // All paths are of course the subsets of given set because we are 
        // choosing the elements from the given numbers.
        answer.push_back(path); // add current subset into answer.
        
        for (int i=startIndex; i<numbers.size(); i++) { // for each possibility.
            path.push_back(numbers[i]); // consider this possibility.
            recurse(path, i+1); // to avoid choosing same number multiple
                                // times, move the startIndex by 1.
            path.pop_back(); // undo the considered possibility.
        }
    }
    
public:
    vector<vector<int>> subsets(vector<int>& nums) {
        numbers = nums;
        vector<int> path; // to store the subset. Initially empty.
        recurse(path, 
               0); // what index to start from.
        return answer;
    }
};