# C++_AC_DFS + Trie (Prefix Tree)

• The main problem of this question is how to avoid the duplicate result in our algorithms, so I used Trie to check it. My method may not be the most efficient, but just have a try. LOL
I also see that lots of people use hash set to solve this problem, thats great!!

``````class Node{
public:
unordered_map<int, Node*> mp;
bool isEnd = false;
};

class Solution {
public:
Node node;
bool find(vector<int>& nums){
Node* tmp_node = &node;
for(int i = 0; i < nums.size(); ++i){
if(tmp_node->mp.find(nums[i]) == tmp_node->mp.end()){
return false;
}else{
tmp_node = tmp_node->mp[nums[i]];
}
}
return tmp_node->isEnd;
}

Node* tmp_node = &node;
for(int i = 0; i < nums.size(); ++i){
if(tmp_node->mp.find(nums[i]) != tmp_node->mp.end()){
tmp_node = tmp_node->mp[nums[i]];
}else{
tmp_node->mp[nums[i]] = new Node();
tmp_node = tmp_node->mp[nums[i]];
}
}
tmp_node->isEnd = true;
}
vector<vector<int>> findSubsequences(vector<int>& nums) {
vector<vector<int>> res;
if(nums.empty()) return res;
vector<int> path;
for(int i = 0; i < nums.size(); ++i){
path.push_back(nums[i]);
dfs(nums, res, i + 1, path);
path.pop_back();
}
return res;
}

void dfs(vector<int>& nums, vector<vector<int>>& res, int pos, vector<int>& path){
if(pos >= nums.size()) return;
for(int i = pos; i < nums.size(); ++i){
if(nums[i] >= path.back()){
path.push_back(nums[i]);
if(!find(path)){
res.push_back(path);