leetcode 39. Combination Sum

dfs是比较简单的做法。。但总觉得会有类似的数学公式或者关系之类的

    vector<vector<int>> ans;    vector<int> newsequece;    int aim;    void dfs(int sum, int i, vector<int>& temp)    {        if (sum == aim)        {            ans.push_back(temp);                //以前在这儿加了一句pop，但这不能说不对，但会少考虑情况，不容易想全                return;         }        if (sum>aim)            return;                           //和上面情况相同，也曾加了一句pop        for (int j = i; j < newsequece.size(); j++)        {            if (sum + newsequece[j] > aim)            {                return;            }            temp.push_back(newsequece[j]);            dfs(sum + newsequece[j], j, temp);            temp.pop_back();           //在这儿加比较好        }    }    vector<vector<int>> combinationSum(vector<int>& candidates, int target)     {        aim = target;        sort(candidates.begin(), candidates.end());        for (int i = 0; i < candidates.size(); i++)            if (candidates[i] <= target)                newsequece.push_back(candidates[i]);        vector<int> temp;        dfs(0, 0, temp);        return ans;    }