Word Search - LeetCode

Given a 2D board and a word, find if the word exists in the grid.

The word can be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontally or vertically neighboring. The same letter cell may not be used more than once.

Example:

board =
[
  ['A','B','C','E'],
  ['S','F','C','S'],
  ['A','D','E','E']
]

Given word = "ABCCED", return true.
Given word = "SEE", return true.
Given word = "ABCB", return false.

Java Solution :

class Solution {
    public boolean exist(char[][] board, String word) {
        if(board == null || word == null)
            return true;
        for(int i =0 ; i < board.length; i++){
            for(int j=0; j < board[i].length ; j++){
                if(board[i][j] == word.charAt(0) && dfs(board,i,j,0,word))
                    return true;
            }
        }
        return false;
    }
    
    public boolean dfs(char[][] board,int i , int j, int count,String word){
        if(count == word.length())
            return true;
        
        if(i<0 || i >=board.length || j<0 || j>= board[i].length || board[i][j] != word.charAt(count) ){
            return false;
        }
        
        char temp = board[i][j];
        board[i][j] = ' ';
        boolean found = dfs(board,i+1,j,count+1,word) || dfs(board,i-1,j,count+1,word) || dfs(board,i,j+1,count+1,word) || dfs(board,i,j-1,count+1,word);
        board[i][j]= temp;
        
        return found;
    }
}