<p>Given an <code>m x n</code> <code>board</code>&nbsp;of characters and a list of strings <code>words</code>, return <em>all words on the board</em>.</p>

<p>Each word must be constructed from letters of sequentially adjacent cells, where <strong>adjacent cells</strong> are horizontally or vertically neighboring. The same letter cell may not be used more than once in a word.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/11/07/search1.jpg" style="width: 322px; height: 322px;" />
<pre>
<strong>Input:</strong> board = [[&quot;o&quot;,&quot;a&quot;,&quot;a&quot;,&quot;n&quot;],[&quot;e&quot;,&quot;t&quot;,&quot;a&quot;,&quot;e&quot;],[&quot;i&quot;,&quot;h&quot;,&quot;k&quot;,&quot;r&quot;],[&quot;i&quot;,&quot;f&quot;,&quot;l&quot;,&quot;v&quot;]], words = [&quot;oath&quot;,&quot;pea&quot;,&quot;eat&quot;,&quot;rain&quot;]
<strong>Output:</strong> [&quot;eat&quot;,&quot;oath&quot;]
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/11/07/search2.jpg" style="width: 162px; height: 162px;" />
<pre>
<strong>Input:</strong> board = [[&quot;a&quot;,&quot;b&quot;],[&quot;c&quot;,&quot;d&quot;]], words = [&quot;abcb&quot;]
<strong>Output:</strong> []
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>m == board.length</code></li>
	<li><code>n == board[i].length</code></li>
	<li><code>1 &lt;= m, n &lt;= 12</code></li>
	<li><code>board[i][j]</code> is a lowercase English letter.</li>
	<li><code>1 &lt;= words.length &lt;= 3 * 10<sup>4</sup></code></li>
	<li><code>1 &lt;= words[i].length &lt;= 10</code></li>
	<li><code>words[i]</code> consists of lowercase English letters.</li>
	<li>All the strings of <code>words</code> are unique.</li>
</ul>

class Solution {
public:
    class Node{
        public:
            vector<Node* > children;
            bool eow=false;

            Node(){
                for(int i=0; i<26; i++) children.push_back(nullptr);
            }
    };
    void dfs(vector<vector<char>>& board, Node* root1, set<string>& ans,int i, int j,vector<vector<int>>& marked,string s){
        marked[i][j]=1;
        s.push_back(board[i][j]);
        // cout<<"string: "<<s<<endl;
        if(root1->eow==true) ans.insert(s);
        // cout<<"mm "<<marked[i][j]
        if(i>0 && marked[i-1][j]==0){
           
            if(root1->children[board[i-1][j]-'a']!=nullptr){
                dfs(board,root1->children[board[i-1][j]-'a'],ans,i-1,j,marked,s);
                marked[i-1][j]=0;
            }
        }
        if(j>0 && marked[i][j-1]==0){
            
            if(root1->children[board[i][j-1]-'a']!=nullptr){
                dfs(board,root1->children[board[i][j-1]-'a'],ans,i,j-1,marked,s);
                marked[i][j-1]=0;
            }
        }
        if(i<board.size()-1 && marked[i+1][j]==0){
           
            if(root1->children[board[i+1][j]-'a']!=nullptr){
                dfs(board,root1->children[board[i+1][j]-'a'],ans,i+1,j,marked,s);
                marked[i+1][j]=0;
            }
        }
        if(j<board[0].size()-1 && marked[i][j+1]==0){
           
            if(root1->children[board[i][j+1]-'a']!=nullptr){
                dfs(board,root1->children[board[i][j+1]-'a'],ans,i,j+1,marked,s);
                marked[i][j+1]=0;
            }
        }
        
    }
    vector<string> findWords(vector<vector<char>>& board, vector<string>& words) {
        Node* root=new Node();
        Node* curr=root;

        for(int i=0; i<words.size(); i++){
            for(int j=0; j<words[i].size(); j++){
                if(curr->children[words[i][j]-'a']==nullptr){
                    curr->children[words[i][j]-'a']=new Node();
                }
                if(j==words[i].size()-1) curr->children[words[i][j]-'a']->eow=true;
                curr=curr->children[words[i][j]-'a'];
            }
            curr=root;
        }
        set<string>ans;
        
        
        for(int i=0; i<board.size(); i++){
            for(int j=0; j<board[0].size(); j++){
                string s="";
                if(root->children[board[i][j]-'a']!=nullptr){
                    // cout<<board[i][j]<<endl;
                    vector<vector<int>>marked(board.size(),vector<int>(board[0].size()));
                    dfs(board,root->children[board[i][j]-'a'],ans,i,j,marked,s);
                }
                
            }
        }

        vector<string>v;
        for(auto& x:ans){
            v.push_back(x);
        }
        return v;
    }
};
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