class Solution {
public:
     bool dfs(vector< vector<char> >&board, int i, int j, int index, string& word){

        //NULL case
        if(i < 0 || i >= board.size() || j < 0 || j >= board.size() || board[i][j] == '*')
            return false;
        if(board[i][j] != word[index] || index >= word.length())
            return false;
        if(index == word.length() - 1)
            return true;

        char temp = board[i][j];
        board[i][j] = '*';

        bool ans = dfs(board, i + 1, j, index + 1, word) || dfs(board, i - 1, j, index + 1, word)
                        || dfs(board, i, j + 1, index + 1, word) || dfs(board, i, j - 1, index + 1, word);

        board[i][j] = temp;
        return ans;


    }

    bool exist(vector<vector<char>>& board, string word) {
        for(size_t i = 0; i < board.size(); i++){
            for(size_t j = 0; j < board[i].size(); j++){
                if(dfs(board, i, j, 0, word)){
                        return true;
                    }
                }
            }

        return false;

    }
};