leetcode - 79. Word Search

class Solution {
public:
    bool visit(vector<vector<char>>& board, string & word,int i,int j,int n,bool **p)
    {
        if(p[i][j]) return 0;
        if(word[n]!=board[i][j]) return 0;
        if(n==word.size()-1) return 1;
        p[i][j]=1;
        if(i)
        {
            
            if(visit(board,word,i-1,j,n+1,p)) return 1;
        }
        if(j)
        {
            if(visit(board,word,i,j-1,n+1,p)) return 1;
        }
        if(j<(board[0].size()-1)) 
        {
            if(visit(board,word,i,j+1,n+1,p)) return 1;
        }
        if(i<(board.size()-1)) 
        {
            if(visit(board,word,i+1,j,n+1,p)) return 1;
        }
        p[i][j]=0;
        return 0;
    }
    bool exist(vector<vector<char>>& board, string word) {
        int m=board.size();
        if(!m) return 0;
        int n=board[0].size();
        bool *p[m];
        for(int i=0;i<m;++i)
        {
            p[i]=new bool[n];
            fill(p[i],p[i]+n,0);
        }
        for(int i=0;i<m;++i)
        {
            for(int j=0;j<n;++j)
            {
                if(visit(board,word,i,j,0,p))
                    return 1;
            }
        }
        return 0;
    }
};