<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:
    int tr[30003 * 10][26];
    int cnt[30003], idx = 0;
    int m, n;
    string ma[10003];
    int dirs[4][2] =  {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
    vector<string> res;

    // int visited[12][12];
    void ins(string word)
    {
        int p = 0;
        for (char c : word)
        {
            int x =  c - 'a';
            if (tr[p][x] == 0) tr[p][x] = ++idx;
            p = tr[p][x];
        }
        cnt[p] = 1;
        ma[p] = word;
    }
    void dfs(int p, int i, int j, vector<vector<char>> & board)
    {
        if (board[i][j] == '*') return;
        int x = board[i][j] - 'a';
        if (tr[p][x] == 0)
            return;
        else
        {
            // visited[i][j] = 1;
            char ch = board[i][j];
            board[i][j] = '*';
            p = tr[p][x];
            if (cnt[p]) 
            {
                res.push_back(ma[p]);
                cnt[p] = 0;
            }
            for (auto d : dirs)
            {
                int a = i + d[0], b = j + d[1];
                if (a < 0 || a == n || b < 0 || b == m) continue;
                
                if (board[a][b]!= '*')
                    dfs(p, a, b, board);
            }
            // visited[i][j] = 0;
            board[i][j] = ch;
        }
    }
    vector<string> findWords(vector<vector<char>>& board, vector<string>& words) {
        memset(tr, 0, sizeof tr);
        memset(cnt,0 ,sizeof cnt);
        idx = 0;
        n = board.size();
        m = board[0].size();
        for (string w : words) ins(w);
        res.clear();
        for (int i = 0; i < n; i++)
        {
            for (int j = 0; j < m; j++)
            {
                // memset(visited, 0, sizeof visited);
                dfs(0, i, j, board);
            }
        }
        // vector<string> res;
        return res;
    }
};
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