Subset

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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。

 1 class Solution { 2 private: 3     vector<vector<int> > ret; 4 public: 5     void dfs(int dep, int maxDep, vector<int> &num, vector<int> a, int start) 6     { 7         ret.push_back(a); 8          9         if (dep == maxDep)10             return;11             12         for(int i = start; i < num.size(); i++)13         {14             vector<int> b(a);15             b.push_back(num[i]);16             dfs(dep + 1, maxDep, num, b, i + 1);17         }18     }19     20     vector<vector<int> > subsets(vector<int> &S) {21         // Start typing your C/C++ solution below22         // DO NOT write int main() function23         sort(S.begin(), S.end());24         ret.clear();25         vector<int> a;26         dfs(0, S.size(), S, a, 0);27         28         return ret;29     }30 };