[Leetcode] Subsets II

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],
  []
]

这道题用了combination的DFS模板加上一个for循环，加了一个used的bool型数组避免重复。

第一遍做这道题的时候很suffer，完全没往combination上去想，果然训练多了还是有一点小长进。

class Solution {
public:
    vector<vector<int> > subsetsWithDup(vector<int> &S) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<int> answer;
        vector<vector<int> > result;
        result.push_back(answer); //empty set
        sort(S.begin(), S.end());
        int maxDep;
        for(int i = 1;i<=S.size();i++)
        {
            answer.clear();
            vector<bool> used(S.size(),false);
            dfs(result,answer,S,used,0,0,i);
        }
        return result;
    }
    
    void dfs(vector<vector<int> > &result, vector<int> &answer, vector<int> &num, vector<bool> used, int depth,int index, int maxDepth)
    {
        if(depth==maxDepth)
        {
            result.push_back(answer);
            return;
        }
        
        for(int i=index;i<num.size();i++)
        {
            if(i!=0&&num[i]==num[i-1]&&used[i-1]==false)
            {
                continue;   //avoid duplicates             
            }
            else
            {
                answer.push_back(num[i]);
                used[i]=true;
                dfs(result,answer,num,used,depth+1,i+1,maxDepth);
                answer.pop_back();
                used[i]=false;                
            }
        }
        
    }
};