LeetCode 79. Word Search

class Solution {
public:
    int di[4]={0,0,1,-1};
    int dj[4]={1,-1,0,0};
    
    bool exist(vector<vector<char>>& board, string word) {
        for (int i=0;i<board.size();++i){
            for (int j=0;j<board[0].size();++j){
                if (dfs(board,i,j,word,0)) return true;
            }
        }
        return false;
    }
    
    bool dfs(vector<vector<char>> &board, int i, int j, string &word, int index){if (i<0||i>=board.size()||j<0||j>=board[0].size()||board[i][j]!=word[index]) 
            return false;
        if (index==word.size()-1) return true;
        
        char copy=board[i][j];
        board[i][j] = ‘#‘;
        
        bool tmp=false;
        for (int k=0;k<4;++k){
            if (dfs(board,i+di[k],j+dj[k],word,index+1)){
                tmp = true;
                break;
            }
        }
        board[i][j] = copy;
        return tmp;
    }
};