<p>Given an <code>m x n</code> grid of characters <code>board</code> and a string <code>word</code>, return <code>true</code> <em>if</em> <code>word</code> <em>exists in the grid</em>.</p>

<p>The word can be constructed from letters of sequentially adjacent cells, where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/11/04/word2.jpg" style="width: 322px; height: 242px;" />
<pre>
<strong>Input:</strong> board = [[&quot;A&quot;,&quot;B&quot;,&quot;C&quot;,&quot;E&quot;],[&quot;S&quot;,&quot;F&quot;,&quot;C&quot;,&quot;S&quot;],[&quot;A&quot;,&quot;D&quot;,&quot;E&quot;,&quot;E&quot;]], word = &quot;ABCCED&quot;
<strong>Output:</strong> true
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/11/04/word-1.jpg" style="width: 322px; height: 242px;" />
<pre>
<strong>Input:</strong> board = [[&quot;A&quot;,&quot;B&quot;,&quot;C&quot;,&quot;E&quot;],[&quot;S&quot;,&quot;F&quot;,&quot;C&quot;,&quot;S&quot;],[&quot;A&quot;,&quot;D&quot;,&quot;E&quot;,&quot;E&quot;]], word = &quot;SEE&quot;
<strong>Output:</strong> true
</pre>

<p><strong class="example">Example 3:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/10/15/word3.jpg" style="width: 322px; height: 242px;" />
<pre>
<strong>Input:</strong> board = [[&quot;A&quot;,&quot;B&quot;,&quot;C&quot;,&quot;E&quot;],[&quot;S&quot;,&quot;F&quot;,&quot;C&quot;,&quot;S&quot;],[&quot;A&quot;,&quot;D&quot;,&quot;E&quot;,&quot;E&quot;]], word = &quot;ABCB&quot;
<strong>Output:</strong> false
</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;= 6</code></li>
	<li><code>1 &lt;= word.length &lt;= 15</code></li>
	<li><code>board</code> and <code>word</code> consists of only lowercase and uppercase English letters.</li>
</ul>

<p>&nbsp;</p>
<p><strong>Follow up:</strong> Could you use search pruning to make your solution faster with a larger <code>board</code>?</p>

class Solution {
public:
    bool solve(vector<vector<char>>& board, string& word, int pointer, int i, int j, int n, int m, vector<vector<bool>>& visited,vector<vector<int>>& dir) {
        if (pointer == word.size()) return true;
        if (i < 0 || i >= n || j < 0 || j >= m || board[i][j] != word[pointer] || visited[i][j]) return false;
        visited[i][j] = true;
        for (auto d : dir) {
            if (solve(board, word, pointer + 1, i+d[0], j+d[1], n, m, visited,dir)) {
                return true;
            }
        }
        visited[i][j] = false;
        return false;
    }

    bool exist(vector<vector<char>>& board, string word) {
        int n = board.size();
        int m = board[0].size();
                vector<vector<int>> dir = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
        vector<vector<bool>> visited(n, vector<bool>(m, false));
        unordered_map<char,int> mp;
        for(auto r:board) {
            for(auto c:r) mp[c]++;
        }
        for(auto c:word) {
            mp[c]-=1;
            if(mp[c]<0) return false;
        }
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (solve(board, word, 0, i, j, n, m, visited,dir)) return true;
            }
        }
        return false;
    }
};

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