<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 {
    struct TrieNode {
        char ch;
        bool leaf;
        std::vector<std::shared_ptr<TrieNode>> children;

        explicit TrieNode(char c) : ch(c), leaf(false), children(26, nullptr) {}
    };

    std::shared_ptr<TrieNode> ConstructTree(const std::vector<std::string> &words) {
        std::shared_ptr<TrieNode> root(new TrieNode('\0'));
        for (auto &&word: words) {
            auto p = root;
            for (auto &&ch: word) {
                auto index = ch - 'a';
                if (p->children[index] == nullptr) {
                    p->children[index].reset(new TrieNode(ch));
                }
                p = p->children[index];
            }
            p->leaf = true;
        }
        return root;
    }

    void dfs(std::shared_ptr<TrieNode> root, std::vector<std::string> *found_words, std::string *current,
             const std::vector<std::vector<char>> &board, int row, int col, std::vector<std::vector<bool>> *visited) {
        if ((*visited)[row][col]) {
            return;
        }
        current->push_back(board[row][col]);
        (*visited)[row][col] = true;
        auto child = root->children[board[row][col] - 'a'];
        if (child == nullptr) {
            current->pop_back();
            (*visited)[row][col] = false;
            return;
        }
        if (child->leaf) {
            found_words->push_back(*current);
            child->leaf = false;
        }
        if (row > 0) {
            dfs(child, found_words, current, board, row - 1, col, visited);
        }
        if (row < board.size() - 1) {
            dfs(child, found_words, current, board, row + 1, col, visited);
        }
        if (col > 0) {
            dfs(child, found_words, current, board, row, col - 1, visited);
        }
        if (col < board[row].size() - 1) {
            dfs(child, found_words, current, board, row, col + 1, visited);
        }
        current->pop_back();
        (*visited)[row][col] = false;
    }

public:
    std::vector<std::string>
    findWords(const std::vector<std::vector<char>> &board, const std::vector<std::string> &words) {
        auto root = ConstructTree(words);
        std::vector<std::string> found_words;
        std::string current;
        std::vector<std::vector<bool>> visited(board.size(), std::vector<bool>(board[0].size()));
        for (int i = 0; i < board.size(); ++i) {
            for (int j = 0; j < board[i].size(); ++j) {
                dfs(root, &found_words, &current, board, i, j, &visited);
            }
        }
        return found_words;
    }
};
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