<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>

struct TrieNode {
    bool isWordEnd = false;
    int indx;
    TrieNode* children[26];

};

class Trie {
    TrieNode* root = new TrieNode();

public:
    Trie()  {}
    
    void insert(const string& word, int indx) {
        auto node =  root;
        for(auto c: word)
        {
            auto indx = c-'a';
            if(!node->children[indx]) node->children[indx] = new TrieNode{};
            node = node->children[indx];
        }

        node->isWordEnd = true;
        node->indx = indx;
    }
    
    bool search(const string& word) {
        auto node =  root;
        for(auto c: word)
        {
            auto indx = c-'a';
            if(!node->children[indx]) return false;
            node = node->children[indx];
        }
        return node->isWordEnd;
    }



    void dfs(const vector<vector<char>>& board, vector<vector<int>>& visited, TrieNode* node, int j, int k, unordered_set<int>& ans, string& word)
    {
        visited[j][k] = 1;

        if(node->isWordEnd)
        {
            ans.insert(node->indx);
        }

        for(int i=0; i<26; i++)
        {
            char c = i+'a';
            if(node->children[i])
            {

                auto child = node->children[i];
                word += c;
                                                                    // cout << word <<endl;

                if(j>0 && board[j-1][k] == c && !visited[j-1][k])
                {
                    dfs(board, visited, child, j-1, k, ans, word);
                }

                if(j+1<board.size() && board[j+1][k] == c && !visited[j+1][k])
                {
                    dfs(board, visited, child, j+1, k, ans, word);
                }
                
                if(k>0 && board[j][k-1] == c && !visited[j][k-1])
                {
                    dfs(board, visited, child, j, k-1, ans, word);
                }

                if (k+1<board[0].size() && board[j][k+1] == c && !visited[j][k+1])
                {
                    dfs(board, visited, child, j, k+1, ans, word);
                }
            }
        }

        visited[j][k] = 0;
    }

    void find(const vector<vector<char>>& board, unordered_set<int>& ans)
    {
        vector<vector<int>> visited(board.size(), vector<int>(board[0].size(), 0));
        auto node = root;
        for(int i=0; i<26; i++)
        {
            if(node->children[i])
            {
                char c = i+'a';
                for(int j=0; j<board.size(); j++)
                {
                    for(int k=0; k<board[0].size(); k++)
                    {
                        if(board[j][k] == c)
                        {
                            cout << c << ", " << i << board[j][k] << endl;
                            string word;
                            word += c;

                            
                            dfs(board, visited, node->children[i], j, k, ans, word);
                        }   
                    }
                }
            }
        }

    }
};

class Solution {

public:
    vector<string> findWords(vector<vector<char>>& board, vector<string>& words) {
        Trie dict{};
        for(int i=0; i<words.size(); i++) dict.insert(words[i], i);

        vector<string> ans;
        unordered_set<int> string_index;
        dict.find(board, string_index);
        for(auto indx: string_index)
            ans.emplace_back(words[indx]);

      
        return ans;
    }
};
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