代码随想录算法训练营第二十四天| 491.递增子序列 46.全排列 47.全排列 II

 491.递增子序列 

此题的难点：

1，前提需要保留原有顺序

2，保证递增

3，保证去重

注意：

去重一定要有set的同时保证有顺序

代码：

 1 void findSubsequences_trackBack(vector<int>& nums, int startIndex, vector<int>& path, vector<vector<int>>& result)
 2 {
 3     if (path.size() >= 2 )
 4     {
 5         result.push_back(path);
 6     }
 7 
 8     unordered_set<int> selected;
 9     for (int i = startIndex; i < nums.size(); i++)
10     {
11         if (selected.find(nums[i]) != selected.end() || (path.size() > 0 && nums[i] < path.back()))
12         {
13             continue;
14         }
15         selected.insert(nums[i]);
16         path.push_back(nums[i]);
17         findSubsequences_trackBack(nums, i + 1, path, result);
18         path.pop_back();
19     }
20 
21 }
22 vector<vector<int>> findSubsequences(vector<int>& nums) {
23     vector<vector<int>> result;
24     if (nums.size() == 0) return result;
25 
26     vector<int>path;
27     findSubsequences_trackBack(nums, 0, path, result);
28     return result;
29 }