<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:
    def findWords(self, board: List[List[str]], words: List[str]) -> List[str]:
    
        def dfs(i,j,n,w,d):
            if((i,j) in d and d[(i,j)]==1):
                return False
            if board[i][j]!=w[n]:
                return False
            else:
                if n==len(w)-1:
                    return True

                d[(i,j)]=1
                if i+1 < len(board):
                    if dfs(i+1,j,n+1,w,d):
                        return True
                if i-1 >= 0:
                    if dfs(i-1,j,n+1,w,d):
                        return True
                if j+1 < len(board[0]):
                    if dfs(i,j+1,n+1,w,d):
                        return True
                if j-1 >= 0:
                    if dfs(i,j-1,n+1,w,d):
                        return True
                d[(i,j)]=0
                return False
        complete=[]
        
        letters_set = dict()
        for i in range(len(board)):
            for j in range(len(board[0])):
                letters_set[board[i][j]]=1
        for w in words:
            do_rev=False
            if len(w)>5:
                count=0
                for i in range(1,len(w)):
                    if w[i]==w[i-1]:
                        count+=1
                    else:
                        if count>5:
                            do_rev=True
                        break
            if do_rev:
                w=list(w)
                w.reverse()
                w = ''.join(w)
            flag=0
            for i in range(len(w)):
                if w[i] not in letters_set:
                    flag=1
                    break
            if flag:
                continue
            for i in range(len(board)):
                for j in range(len(board[0])):
                    if dfs(i,j,0,w,dict()):
                        if do_rev:
                            w=list(w)
                            w.reverse()
                            w = ''.join(w)
                        complete.append(w)
                        flag=1
                        break
                if flag:
                    break
                    

        return complete
16800