[LeetCode]Subsets II

原题链接：http://oj.leetcode.com/problems/subsets-ii/

题意描述：

Given a collection of integers that might contain duplicates, 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 = [1,2,2], a solution is:

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

题解：

　　这题是含重复元素的子集生成，简化版本是集合中无重复元素，见http://www.cnblogs.com/codershell/p/3619928.html，

　　我在《子集问题（寻找给定集合的所有子集）》一文中详细分析了子集问题，具体解释不再赘述。

class Solution {
public:
    bool isExist(vector<vector<int> > &vv,vector<int> v){
        for(int i=0; i<vv.size(); i++)
            if(vv[i] == v)
                return true;
                
        return false;
    }
    
    void ss(vector<vector<int> > &vv,int* flag,int n, vector<int> &S, int cur){
        if(cur == n){
            vector<int> v;
            for(int i = 0; i < cur; i++)
                if(flag[i])
                    v.push_back(S[i]);
            if(!isExist(vv,v))
                vv.push_back(v);
            return;
        }
        
        flag[cur] = 1;                                // 选第 cur 个元素
        ss(vv,flag,n, S, cur+1);
        flag[cur] = 0;                                // 不选第 cur 个元素
        ss(vv,flag,n, S, cur+1);
    }
    
    vector<vector<int> > subsetsWithDup(vector<int> &S) {
        int *flag = (int *)malloc(sizeof(int) * S.size()) ;
        
        vector <vector<int>> array;
        sort(S.begin(),S.end());
        ss(array,flag,S.size(),S,0);
        free(flag);
        return array;
    }
};