[Leetcode 64] 78 Subsets

Problem:

Given a set of distinct integers, S, return all possible subsets.

Note:

• Elements in a subset must be in non-descending order.
• The solution set must not contain duplicate subsets.

 

For example,
If S = [1,2,3], a solution is:

[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

 

Analysis:

Simple backtracking problem.

 

Code:

class Solution {
public:
    vector<vector<int> > res;

    vector<vector<int> > subsets(vector<int> &S) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        res.clear();
        sort(S.begin(), S.end());
        vector<int> path;
        for (int i=0; i<=S.size(); i++)
            bc(0, path, S, i);
        
        return res;
    }
    
    void bc(int idx, vector<int> path, vector<int> &s, int setSize) {
        if (path.size() == setSize) {
            res.push_back(path);
            return ;
        }
        
        for (int i=idx; i<s.size(); i++) {
            path.push_back(s[i]);
            bc(i+1, path, s, setSize);
            path.pop_back();
        }
        
        return ;
    }
};