<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 Trie:
    def __init__(self):
        self.wordValue = ""
        self.nxt = [None] * 26

class Solution:
    def findWords(self, board: List[List[str]], words: List[str]) -> List[str]:
        self.N = len(board)
        self.M = len(board[0])
        self.ans = []  
        word_set = set(words)

        dxy = [(0, 1), (1, 0), (0, -1), (-1, 0)]  
        root = Trie()

        for word in word_set:
            cur = root
            for character in word:
                ch = ord(character) - ord('a')
                if cur.nxt[ch] == None:
                    cur.nxt[ch] = Trie()
                cur = cur.nxt[ch]
            cur.wordValue = word

        def dfs(x, y, node):
            ch = ord(board[x][y]) - ord('a')
            if node.nxt[ch] == None:
                return
            node = node.nxt[ch]

            if node.wordValue:
                self.ans.append(node.wordValue)
                node.wordValue = ""

            board[x][y] = '$'

            for dx, dy in dxy:
                nx, ny = x + dx, y + dy
                if 0 <= nx < self.N and 0 <= ny < self.M and board[nx][ny] != '$':
                    dfs(nx, ny, node)

            board[x][y] = chr(ch + ord('a'))            

        for i in range(self.N):
            for j in range(self.M):
                dfs(i, j, root)

        return self.ans
18600