1009 word search

The title is as follows

Given a m x n Two dimensional character grid board And a string word word . If word Exists in the grid , return true ; otherwise , return false .

The words must be in alphabetical order , It's made up of letters in adjacent cells , among “ adjacent ” Cells are those adjacent horizontally or vertically . Letters in the same cell are not allowed to be reused .

Example 1：

Input ：board = [[“A”,“B”,“C”,“E”],[“S”,“F”,“C”,“S”],[“A”,“D”,“E”,“E”]], word = “ABCCED”
Output ：true

Example 2：

Input ：board = [[“A”,“B”,“C”,“E”],[“S”,“F”,“C”,“S”],[“A”,“D”,“E”,“E”]], word = “SEE”
Output ：true

Example 3：

Input ：board = [[“A”,“B”,“C”,“E”],[“S”,“F”,“C”,“S”],[“A”,“D”,“E”,“E”]], word = “ABCB”
Output ：false

How to solve the problem

class Solution 
{
    
public:
    bool check(vector<vector<char>>& board, vector<vector<int>>& visited, int i, int j, string& s, int k) 
    {
    
        if (board[i][j] != s[k]) 
        {
    
            return false;
        }
        else if (k == s.length() - 1) 
        {
    
            return true;
        }
        visited[i][j] = true;
        vector<pair<int, int>> directions{
     {
    0, 1}, {
    0, -1}, {
    1, 0}, {
    -1, 0} };
        bool result = false;
        for (const auto& dir : directions) 
        {
    
            int newi = i + dir.first, newj = j + dir.second;
            if (newi >= 0 && newi < board.size() && newj >= 0 && newj < board[0].size()) 
            {
    
                if (!visited[newi][newj]) 
                {
    
                    bool flag = check(board, visited, newi, newj, s, k + 1);
                    if (flag) 
                    {
    
                        result = true;
                        break;
                    }
                }
            }
        }
        visited[i][j] = false;
        return result;
    }

    bool exist(vector<vector<char>>& board, string word) 
    {
    
        int h = board.size(), w = board[0].size();
        vector<vector<int>> visited(h, vector<int>(w));
        for (int i = 0; i < h; i++) 
        {
    
            for (int j = 0; j < w; j++) 
            {
    
                bool flag = check(board, visited, i, j, word, 0);
                if (flag) 
                {
    
                    return true;
                }
            }
        }
        return false;
    }
};