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