在递归中查找矩阵中的路径

def exist(matrix, word):
    if not matrix or not matrix[0]:
        return False
    
    rows, cols = len(matrix), len(matrix[0])
    visited = [[False] * cols for _ in range(rows)]
    
    for i in range(rows):
        for j in range(cols):
            if dfs(matrix, word, visited, i, j, 0):
                return True
    
    return False

def dfs(matrix, word, visited, row, col, index):
    if index == len(word):
        return True
    
    if (row < 0 or row >= len(matrix) or col < 0 or col >= len(matrix[0]) or
        visited[row][col] or matrix[row][col] != word[index]):
        return False
    
    visited[row][col] = True
    
    if (dfs(matrix, word, visited, row - 1, col, index + 1) or
        dfs(matrix, word, visited, row + 1, col, index + 1) or
        dfs(matrix, word, visited, row, col - 1, index + 1) or
        dfs(matrix, word, visited, row, col + 1, index + 1)):
        return True
    
    visited[row][col] = False
    
    return False