78. Subsets (Back-Track, DP)

Given a set of distinct integers, nums, 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 nums = [1,2,3], a solution is:

[

  [3],

  [1],

  [2],

  [1,2,3],

  [1,3],

  [2,3],

  [1,2],

  []

]

思路：遍历数组，有选择当前元素和不选当前元素两种操作，所以使用带回溯的递归

class Solution {

public:

    vector<vector<int>> subsets(vector<int> &S) {

        vector<vector<int>> result;

        vector<int> pre;

        result.push_back(pre);

        if(S.size()==)

            return result;

        sort(S.begin(),S.end());

        DepthFirst(S,result,pre,);

        return result;

    }

    void DepthFirst(vector<int> &S , vector<vector<int>> &result ,vector<int> &pre , int depth)

    {

        if (depth==S.size()) {

            return;

        }

        pre.push_back(S[depth]);

        result.push_back(pre);

        DepthFirst(S,result,pre,depth+);

        pre.pop_back();

        DepthFirst(S,result,pre,depth+);

    }

};

思路II: DP. n个元素的数组结果，是n-1个数组结果，再加上插入第n个元素的结果

class Solution {

public:

    vector<vector<int>> subsets(vector<int>& nums) {

        vector<vector<int>> ret;

        vector<int> retItem;

        ret.push_back(retItem);

        int size; //number of memebers in ret

        for(int i = ; i < nums.size(); i++){ //iterate the number to insert

            size = ret.size();

            for(int j = ; j < size; j++){ //iterate current item in ret

                vector<int> newItem = ret[j];

                newItem.push_back(nums[i]);

                ret.push_back(newItem);

            }

        }

        return ret;

    }

};

巴特西

78. Subsets (Back-Track, DP)

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