<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:
    
    vector<vector<int>> directions{{0,1},{0,-1},{1,0},{-1,0}};
    bool solve(vector<vector<char>>& board,int n,int m,string &word,int i,int j,int ind,int l){
        
        if(ind>=l)return true;
        
        if(i<0 || i>=n || j<0 || j>=m || board[i][j]!=word[ind])
            return false;
        
        char temp=board[i][j];
        board[i][j]='$';
        
        for(auto dir:directions){
            int i_=i+dir[0];
            int j_=j+dir[1];
            if(solve(board,n,m,word,i_,j_,ind+1,l))return true;
        }
        
        
       board[i][j]=temp;
           
           return false;
    }
    bool exist(vector<vector<char>>& board, string word) {
        
        int n=board.size();
        int m=board[0].size();
        
        int l=word.length();
        
        if(m*n < l)
            return false;
        char lastChar = word[l - 1];
        bool lastCharFound = false;
        for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            if (board[i][j] == lastChar) {
                lastCharFound = true;
                break;
            }
        }
        if (lastCharFound) break;
    }
    if (!lastCharFound) return false;
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                if(board[i][j]==word[0] && solve(board,n,m,word,i,j,0,l))
                    return true;
            }
        }
        
        
        return false;
    }
};
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