<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:
    vector<string> findWords(vector<vector<char>>& board, vector<string>& wordList) {
        int n = board.size(), m = board[0].size();
        set<string> words;
        words.insert(wordList.begin(), wordList.end());
        vector<string> res;
        string curr = "";
        vector<string> found;
        set<pair<int,int>> visited;
        function<void(string, int, int)> solve = [&](string curr, int x, int y) {
            if (x < 0 || x >= n || y < 0 || y >= m || visited.count({x,y})) return;
            curr = curr + board[x][y];
            auto p = words.lower_bound(curr);
            if (p == words.end() || p->substr(0,curr.size()) != curr) return;
            if (curr == *p) {
                found.push_back(curr);
                words.erase(curr);
            }
            visited.insert({x, y});
            solve(curr,x-1,y);
            solve(curr,x+1,y);
            solve(curr,x,y-1);
            solve(curr,x,y+1);
            visited.erase({x, y});
        };
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                solve("", i, j);
            }
        }
        return found;
    }
};
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