Word Search

class Solution {public:    bool dfs(int row,int col,int pos,const string& word,const vector<vector<char> >& board,vector<vector<bool> >& visit)    {        if(pos==word.size())        {            return true;        }        int rowDir[]={-1,1,0,0};        int colDir[]={0,0,-1,1};        for(int i=0;i<4;++i)        {            int newRow=row+rowDir[i];            int newCol=col+colDir[i];            if((newRow>=0)&&(newRow<board.size())&&(newCol>=0)&&(newCol<board[0].size())&&!visit[newRow][newCol]&&(board[newRow][newCol]==word[pos]))            {                visit[newRow][newCol]=true;                if(dfs(newRow,newCol,pos+1,word,board,visit)){return true;}                visit[newRow][newCol]=false;            }        }        return false;    }    bool exist(vector<vector<char> > &board, string word) {        if(word.size()==0)        {            return false;        }        int m=board.size();        if(m==0)        {            return false;        }        int n=board[0].size();        if(n==0)        {            return false;        }        if(m*n<word.size())        {            return false;        }        vector<vector<bool> > visit(m,vector<bool>(n,false));        for(int i=0;i<m;++i)        {            for(int j=0;j<n;++j)            {                if(board[i][j]==word[0])                {visit[i][j]=true;                    if(dfs(i,j,1,word,board,visit))                    {                        return true;                    }visit[i][j]=false;                }            }        }        return false;    }};