Leetcode-78. Subsets

题目

Given a set of distinct integers, nums, return all possible subsets.
Note: The solution set must not contain duplicate subsets.
For example,
If nums = [1,2,3], a solution is:
求一个集合的子集

思路

回溯法求子集

代码

class Solution {public:    vector<vector<int> > res;    vector<int> ans;    vector<vector<int> > subsetsWithDup(vector<int>& nums) {        if(nums.size() == 0)            return res;        sort(nums.begin(), nums.end());        dfs(0, ans, nums);//        for(int i=0; i<res.size(); i++) {//            for(int j=0; j<res[i].size(); j++)//                cout << res[i][j] << " ";//            cout << endl;//        }        return res;    }    void dfs(int step, vector<int>& ans, vector<int>& nums) {        res.push_back(ans);        for(int i=step; i<nums.size(); i++) {            ans.push_back(nums[i]);            dfs(i+1, ans, nums);            ans.pop_back();        }    }};