单词搜索.py

# 给定一个二维网格和一个单词，找出该单词是否存在于网格中。
#
# 单词必须按照字母顺序，通过相邻的单元格内的字母构成，其中“相邻”单元格是那些水平相邻或垂直相邻的单元格。同一个单元格内的字母不允许被重复使用。
#
# 示例:
#
# board =
# [
#   ['A','B','C','E'],
#   ['S','F','C','S'],
#   ['A','D','E','E']
# ]
#
# 给定 word = "ABCCED", 返回 true.
# 给定 word = "SEE", 返回 true.
# 给定 word = "ABCB", 返回 false.
from typing import List


class Solution:
    directions = [(0, -1), (-1, 0), (0, 1), (1, 0)]

    def exist(self, board: List[List[str]], word: str) -> bool:
        m = len(board)
        if m == 0:
            return False
        n = len(board[0])

        marked = [[False for _ in range(n)] for _ in range(m)]
        for i in range(m):
            for j in range(n):
                if self.__search_word(board, word, 0, i, j, marked, m, n):
                    return True
        return False

    def __search_word(self, board, word, index, start_x, start_y, marked, m, n):
        if index == len(word) - 1:
            return board[start_x][start_y] == word[index]

        if board[start_x][start_y] == word[index]:
            marked[start_x][start_y] = True
            for direction in self.directions:
                new_x = start_x + direction[0]
                new_y = start_y + direction[1]

                if 0 <= new_x < m and 0 <= new_y < n and not marked[new_x][new_y] and self.__search_word(board, word,
                                                                                                         index + 1,
                                                                                                         new_x, new_y,
                                                                                                         marked, m, n):
                    return True
            marked[start_x][start_y] = False
        return False