[LeetCode] Subsets

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],
  []
]

DFS每次返回当前解，当解深度大于最大深度时返回。

class Solution {
private:
    vector<vector<int> > ret;
public:
    void dfs(int dep, int maxDep, vector<int> &num, vector<int> a, int start)
    {
        ret.push_back(a);
        
        if (dep == maxDep)
            return;
            
        for(int i = start; i < num.size(); i++)
        {
            vector<int> b(a);
            b.push_back(num[i]);
            dfs(dep + 1, maxDep, num, b, i + 1);
        }
    }
    
    vector<vector<int> > subsets(vector<int> &S) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        sort(S.begin(), S.end());
        ret.clear();
        vector<int> a;
        dfs(0, S.size(), S, a, 0);
        
        return ret;
    }
};