<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 {
private:
    struct TrieNode{
        unordered_map<int, TrieNode*> child;
        bool isWord = false;
        string word = "";
    };
    TrieNode* root = new TrieNode(); 
    vector<string> outs;
    int C;
    int R;


public:
    void insert(string &word) {
        TrieNode* temp = root;
        for (int i = 0; i < word.size(); ++i){
            int index = word[i] - 'a';
            if (!temp->child[index]) temp->child[index] = new TrieNode();
            temp = temp->child[index];
        }
        temp->isWord = true;
        temp->word = word;
    }

    bool IsValid(vector<vector<char>>& board, string& word){
        unordered_map<char, int> mp;
        for (auto &c: word) mp[c]++;


        for (int i = 0; i < board.size(); ++i){
            for (int j = 0; j < board[0].size(); ++j){
                mp[board[i][j]]--;
            }
        }

        for (auto i: mp) if (i.second > 0) return false;

        return true;
    }

    vector<string> findWords(vector<vector<char>>& board, vector<string>& words) {

        for (auto &w: words){
            if (IsValid(board, w)) insert(w);
        }

        R = board.size();
        C = board[0].size();


        
        for (int i = 0; i < R; ++i){
            for (int j = 0; j < C; ++j){
                DFS(board, i, j, root);
            }
        }
        return outs;
    }

    void DFS(vector<vector<char>>& board, int i, int j, TrieNode* temp){
        if (min(i, j) < 0 || i >= R || j >= C || !temp->child[board[i][j] - 'a']) return;
        temp = temp->child[board[i][j] - 'a'];
        if (temp->isWord){ 
            outs.emplace_back(temp->word);
            temp->isWord = false;
        }
        char temp_char = board[i][j];
        board[i][j] = '#';
        DFS(board, i + 1, j, temp);
        DFS(board, i - 1, j, temp);
        DFS(board, i, j + 1, temp);
        DFS(board, i, j - 1, temp);
        board[i][j] = temp_char;
    }


};
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