<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:
    vector<string> res;
    vector<vector<int>> dir = {{1,0},{-1,0},{0,1},{0,-1}};
    struct trie
    {
        vector<trie*> child;
        int cnt = 0;
        bool isEnd = false;
        trie()
        {
            child.resize(26,NULL);
        }
    };
    trie* root = new trie();
    void insert(string &word)
    {
        trie* curr = root;
        for(int i=0;i<word.size();i++)
        {
            if(!curr->child[word[i]-'a'])
            {
                curr->cnt++;
                curr->child[word[i]-'a'] = new trie();
            }
            curr = curr->child[word[i]-'a'];
        }
        curr->isEnd = true;
    }
    bool isPresent(string &word)
    {
        trie* curr = root;
        for(int i=0;i<word.size();i++)
        {
            if(!curr->child[word[i]-'a']) return false;
            curr = curr->child[word[i]-'a'];
        }
        return true;
    }
    vector<string> findWords(vector<vector<char>>& board, vector<string>& words) {
        int m = board.size();
        int n = board[0].size();
        for(auto word : words)
        {
            insert(word);
        }
        for(int i=0;i<m;i++)
        {
            for(int j=0;j<n;j++)
            {
                string curr;
                trie* node = root;
                dfs(board,i,j,m,n,curr,node);
            }
        }
        return res;
    }
    void dfs(vector<vector<char>> &board,int r,int c,int m,int n,string &curr,trie* node)
    {
        if(r<0 || c<0 || r>=m || c>=n || board[r][c]=='.' || curr.size()==10 || curr.size()==m*n || node==NULL || node->child[board[r][c]-'a']==NULL)
        {
            return;
        }
        curr.push_back(board[r][c]);
        if(node->child[board[r][c]-'a']->isEnd)
        {
            res.push_back(curr);
            node->child[board[r][c]-'a']->isEnd = false;
        }
        char temp = board[r][c];
        board[r][c] = '.';
        for(auto it : dir)
        {
            int nr = r + it[0];
            int nc = c + it[1];
            dfs(board,nr,nc,m,n,curr,node->child[temp-'a']);
            if(node->child[temp-'a'] && node->child[temp-'a']->cnt==0)
            {
                node->child[temp-'a'] = NULL;
                node->cnt--;
            }
        }
        curr.pop_back();
        board[r][c] = temp;
    }
};
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