leetcode 090 —— Subsets II

Given a collection of integers that might contain duplicates, 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 = [1,2,2], a solution is:

[  [2],  [1],  [1,2,2],  [2,2],  [1,2],  []]

思路：回溯法比较难的一个点，就是怎么防止重复的情况出现，这里用一个record数组记录每个值出现与否，如果前后元素相同，而且前面的元素未被使用，那么说明会出现相同的情况，跳出。

class Solution {public:vector<vector<int>> subsetsWithDup(vector<int>& nums) {vector<vector<int>> res;vector<int> path;vector<bool> record(nums.size(),false);res.push_back(path);sort(nums.begin(), nums.end());dfs(0, path,record, nums, res);return res;}void dfs(int level, vector<int> &path, vector<bool> &record,vector<int> &nums, vector<vector<int>> &res){if (level == nums.size())return;for (int i = level; i < nums.size(); i++){if (i>0 && nums[i] == nums[i - 1]&&!record[i-1])continue;else{record[i] = true;path.push_back(nums[i]);res.push_back(path);dfs(i + 1, path, record,nums, res);path.pop_back();record[i] = false;}}}};