<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:


class TrieNode
{
	public:
		unordered_map<char, TrieNode*> Childs;
		bool IsWord = false;
		string word;
		bool isRemoved = false;

		void insert(string word) {
			auto cur = this;
			for (int i = 0; i < word.size(); i++)
			{
				if (cur->Childs.find(word[i]) == cur->Childs.end())
				{
					auto c = new TrieNode;
					cur->Childs.insert({ word[i], c });
					cur = c;
				}
				else
				{
					cur = cur->Childs[word[i]];
				}
			}
			cur->IsWord = true;
			cur->word = word;
		}

		void remove(string word) {
		auto cur = this;
		TrieNode* lastNodeWithMoreThanOneChild = this;
		int childToRemove = 0;

		for (int i = 0; i < word.size(); i++)
		{
			if (cur->Childs.size() > 1) {
				lastNodeWithMoreThanOneChild = cur;
				childToRemove = i;
			}
			cur = cur->Childs[word[i]];				
		}		

		cur = lastNodeWithMoreThanOneChild;			

		for (int i = childToRemove; i < word.size(); i++)
		{				
			cur = cur->Childs[word[i]];
			cur->isRemoved = true;
		}
	}
};




void DFS(int row, int col, vector<vector<char>>& board, unordered_set<int>& forbidden, TrieNode* trieNode, TrieNode* root, unordered_set<string>& wordsOnTheBoard)
{
	if (trieNode->isRemoved) return;

	if (row < 0 || col < 0 || row >= board.size() || col >= board[0].size()) return;

	int k = row * board[0].size() + col;
	if (forbidden.find(k) != forbidden.end())
	{
		return;
	}	

	char c = board[row][col];
	
	if (trieNode->Childs.find(c) == trieNode->Childs.end())
	{
		return;
	}

	// prefix ist in trie!

	auto parent = trieNode;
	trieNode = trieNode->Childs[c];	
	forbidden.insert(k);
	if (trieNode->IsWord)
	{
		wordsOnTheBoard.insert(trieNode->word);		
		if (trieNode->Childs.size() == 0)
		{
			root->remove(trieNode->word);
		}
	}

	DFS(row + 1, col, board, forbidden, trieNode, root, wordsOnTheBoard);
	DFS(row - 1, col, board, forbidden, trieNode, root, wordsOnTheBoard);
	DFS(row, col + 1, board, forbidden, trieNode, root, wordsOnTheBoard);
	DFS(row, col - 1, board, forbidden, trieNode, root, wordsOnTheBoard);

	trieNode = parent;	
	forbidden.erase(k);
}






    vector<string> findWords(vector<vector<char>>& board, vector<string>& words) {
        auto root = new TrieNode();
        for (auto w : words)
        {
            root->insert(w);
        }

        unordered_set<string> wordsOnTheBoard;
        unordered_set<int> forbidden;	

        for (int i = 0; i < board.size(); i++)
        {
            for (int j = 0; j < board[0].size(); j++)
            {
                DFS(i, j, board, forbidden, root, root, wordsOnTheBoard);
            }
        }

        vector<string> res;
        res.insert(res.end(), wordsOnTheBoard.begin(), wordsOnTheBoard.end());	

        return res;
    }
};
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