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leetcode: Subsets & Subsets II

2024-07-02 14:19:07   215人阅读

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],
  []
]
class Solution {
public:
    vector<vector<int> > subsets(vector<int> &S) {
        sort(S.begin(),S.end());
        vector<int> buf;
        vector<vector<int> > res;
        subset(S,0,buf,res);
        return res;
    }
private:
    void subset(vector<int> &S, int start, vector<int> &buf, vector<vector<int> > &res) {
        if(start == S.size()) {
            res.push_back(buf);
            return;
        }
        
        subset(S,start+1,buf,res);
        
        buf.push_back(S[start]);
        subset(S,start+1,buf,res);
        buf.pop_back();
    }
};

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],
  []
]
class Solution {
public:
    vector<vector<int> > subsetsWithDup(vector<int> &S) {
        sort(S.begin(),S.end());
        vector<int> buf;
        vector<vector<int> > res;
        subset(S,0,buf,res);
        //res.push_back(vector<int> {});
        return res;
        
    }
private:
    void subset(vector<int> &S, int start, vector<int> &buf, vector<vector<int> > &res) {
        if(start == S.size()) {
            res.push_back(buf);
            return;
        }
        int nextStart = distance(S.begin(),upper_bound (S.begin()+start, S.end(), S[start]));
        for(int i=0;i<(nextStart-start);i++) {
            buf.push_back(S[start]);
        }
        for(int i=(nextStart-start);i>0;i--) {
            subset(S,nextStart,buf,res);
            buf.pop_back();
        }
        subset(S,nextStart,buf,res);
    }
};

 

 


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