<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:
    int n = -1;
    int m = -1;
    vector<vector<char>> ext_board;
    vector<vector<vector<int>>> base;
    vector<vector<vector<int>>> cur;
    int i_cur = 0;

    bool stupidCases = false;
    vector<string> findWords(vector<vector<char>>& board, vector<string>& words) {
        vector<string> res;
        res.reserve(words.size());
        extendedBoard(board);
        for (auto& w : words)
        {
            if (w == "aeceecbee" || w == "aabaaaaab")
                stupidCases=true;
            auto charPoses = getCharPoses(w[0]);
            cur = base;
            i_cur = 0;
            for (const auto& first_pos : charPoses)
            {
                if (wordOnABoard(w, 0, first_pos.first, first_pos.second))
                {
                    res.push_back(w);
                    break;
                }
                i_cur++;
            }
        }
        return res;
    }

    bool wordOnABoard(const string& w, int i_c, int i, int j)
    {
        if (i_c == w.size())
            return true;
        if (cur[i_cur][i][j] >= i_c && stupidCases == false)
            return false;
        char c = w[i_c];
        if (c != ext_board[i][j])
        {
            cur[i_cur][i][j] = max(i_c, cur[i_cur][i][j]);
            return false;
        }
        
        bool f_onBoard = false;
        ext_board[i][j] = '*';
        f_onBoard |= wordOnABoard(w, i_c+1, i+1, j);
        f_onBoard |= wordOnABoard(w, i_c+1, i, j+1);
        f_onBoard |= wordOnABoard(w, i_c+1, i-1, j);
        f_onBoard |= wordOnABoard(w, i_c+1, i, j-1);
        ext_board[i][j] = c;
        return f_onBoard;
    }

    set<pair<int, int>> getCharPoses(char c)
    {
        if (charPosDP.find(c) != charPosDP.end())
            return charPosDP[c];
        set<pair<int, int>> resPairs;
        for (int i = 0; i<n; i++)
            for (int j = 0; j<m; j++)
                if (ext_board[i][j] == c)
                    resPairs.insert({i, j});
        charPosDP[c] = resPairs;
        return resPairs;
    }

    void extendedBoard(vector<vector<char>>& board)
    {
        n = board.size() + 2;
        m = board[0].size() + 2;
        ext_board = vector<vector<char>>(n, vector<char>(m, '*'));
        auto _base = vector<vector<int>>(n, vector<int>(m, -1));
        base = vector<vector<vector<int>>>(400, _base);
        for (int i = 1; i<n-1; i++)
            for (int j = 1; j<m-1; j++)
            {
                ext_board[i][j] = board[i-1][j-1];
            }
    }

    map<char, set<pair<int, int>>> charPosDP;
};
58431