leetcode79

class Solution {
    public boolean exist(char[][] board, String word) {
        for(int i=0; i<board.length; i++) {
            for(int j=0; j<board[0].length; j++) {
                if(exist(board, i, j, word, 0))
                    return true;
            }
        }
        return false;
    }
    
    public boolean exist(char[][] board, int x, int y, String word, int index) {
        if(index == word.length()) return true;
        if(x < 0 || y<0 || x>=board.length || y>=board[0].length || board[x][y] != word.charAt(index))
            return false;
            
        board[x][y] ^= 128;
        boolean exist = exist(board, x-1, y, word, index+1) || 
                        exist(board, x+1, y, word, index+1) ||
                        exist(board, x, y-1, word, index+1) ||
                        exist(board, x, y+1, word, index+1) ;
        board[x][y] ^= 128;
        return exist;
    }
}

补充一个python的实现：

class Solution:
    def dfs(self,board,word,index,rows,coloums,visited,i,j):
        if index >= len(word):
            return True
        if i >= rows or i < 0 or j >= coloums or j < 0 or visited[i][j] == 1 or board[i][j] != word[index]:
            return False
        visited[i][j] = 1
        result = self.dfs(board,word,index+1,rows,coloums,visited,i+1,j) or self.dfs(board,word,index+1,rows,coloums,visited,i-1,j) or self.dfs(board,word,index+1,rows,coloums,visited,i,j+1) or self.dfs(board,word,index+1,rows,coloums,visited,i,j-1)

        visited[i][j] = 0

        return result

    def exist(self, board: 'List[List[str]]', word: 'str') -> 'bool':
        rows = len(board)
        coloums = len(board[0])
        visited = [[0 for a in range(coloums)] for b in range(rows)]
        for i in range(rows):
            for j in range(coloums):
                if self.dfs(board,word,0,rows,coloums,visited,i,j):
                    return True
        return False