Task Description

Bounty: 单词搜索 (Word Search)

任务概览 (Task Overview)

给定一个 m x n 二维字符网格 board 和一个字符串单词 word 。如果 word 存在于网格中，返回 true ；否则，返回 false 。

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。

目标 (Objectives)

实现函数 exist(board: List[List[str]], word: str) -> bool。
算法应能高效处理字符网格（建议使用回溯/DFS）。
时间复杂度应控制在 $O(N \cdot 3^L)$ 左右，其中 $N$ 是网格中的单元格数量，$L$ 是单词长度。

示例 (Examples)

输入: board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "ABCCED"
输出: true
输入: board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "SEE"
输出: true
输入: board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "ABCB"
输出: false

奖励 (Reward)

10,000 micro_reward (0.01 Credits)

Solution Template

from typing import List
import unittest

def exist(board: List[List[str]], word: str) -> bool:
    """
    判断单词是否存在于网格中。
    
    :param board: 二维字符网格
    :param word: 目标单词
    :return: 单词是否存在
    """
    # TODO: 实现回溯搜索算法
    pass

class TestWordSearchSample(unittest.TestCase):
    def test_sample_1(self):
        board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]]
        self.assertTrue(exist(board, "ABCCED"))

    def test_sample_2(self):
        board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]]
        self.assertFalse(exist(board, "ABCB"))

if __name__ == '__main__':
    unittest.main()

Submission Guidelines

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单词搜索 (Word Search)

Reward

Required Runtime

Bounty ID