What defines a good line in Check if Move is Legal?

A good line has endpoints of the player's color and consecutive opponent pieces in between, with at least three cells total.

Do I need to check diagonals for legality?

Yes, all eight directions including diagonals must be scanned to confirm a move is legal according to the pattern.

Can the move be legal if it only affects middle cells?

No, the move must be an endpoint of a good line; affecting only middle cells does not qualify as legal.

How does the Array plus Matrix pattern apply here?

The board is a matrix, and you enumerate in array directions from the cell to identify sequences that form good lines.

Is the solution scalable beyond 8x8 boards?

Yes, the same directional scanning approach works, but time complexity increases with board size since more cells must be checked.

#1958

Medium

auto_awesome数组·matrix

LeetCode 题解工作台

检查操作是否合法

给你一个下标从 0 开始的 8 x 8 网格 board ，其中 board[r][c] 表示游戏棋盘上的格子 (r, c) 。棋盘上空格用 '.' 表示，白色格子用 'W' 表示，黑色格子用 'B' 表示。游戏中每次操作步骤为：选择一个空格子，将它变成你正在执行的颜色（要么白色，要么黑色）。但是…

数组矩阵枚举

题目描述

给你一个下标从 0 开始的 8 x 8 网格 board ，其中 board[r][c] 表示游戏棋盘上的格子 (r, c) 。棋盘上空格用 '.' 表示，白色格子用 'W' 表示，黑色格子用 'B' 表示。

游戏中每次操作步骤为：选择一个空格子，将它变成你正在执行的颜色（要么白色，要么黑色）。但是，合法操作必须满足：涂色后这个格子是 好线段的一个端点 （好线段可以是水平的，竖直的或者是对角线）。

好线段 指的是一个包含 三个或者更多格子（包含端点格子）的线段，线段两个端点格子为 同一种颜色 ，且中间剩余格子的颜色都为 另一种颜色 （线段上不能有任何空格子）。你可以在下图找到好线段的例子：

给你两个整数 rMove 和 cMove 以及一个字符 color ，表示你正在执行操作的颜色（白或者黑），如果将格子 (rMove, cMove) 变成颜色 color 后，是一个合法操作，那么返回 true ，如果不是合法操作返回 false 。

示例 1：

输入：board = [[".",".",".","B",".",".",".","."],[".",".",".","W",".",".",".","."],[".",".",".","W",".",".",".","."],[".",".",".","W",".",".",".","."],["W","B","B",".","W","W","W","B"],[".",".",".","B",".",".",".","."],[".",".",".","B",".",".",".","."],[".",".",".","W",".",".",".","."]], rMove = 4, cMove = 3, color = "B"
输出：true
解释：'.'，'W' 和 'B' 分别用颜色蓝色，白色和黑色表示。格子 (rMove, cMove) 用 'X' 标记。
以选中格子为端点的两个好线段在上图中用红色矩形标注出来了。

示例 2：

输入：board = [[".",".",".",".",".",".",".","."],[".","B",".",".","W",".",".","."],[".",".","W",".",".",".",".","."],[".",".",".","W","B",".",".","."],[".",".",".",".",".",".",".","."],[".",".",".",".","B","W",".","."],[".",".",".",".",".",".","W","."],[".",".",".",".",".",".",".","B"]], rMove = 4, cMove = 4, color = "W"
输出：false
解释：虽然选中格子涂色后，棋盘上产生了好线段，但选中格子是作为中间格子，没有产生以选中格子为端点的好线段。

提示：

board.length == board[r].length == 8
0 <= rMove, cMove < 8
board[rMove][cMove] == '.'
color 要么是 'B' 要么是 'W' 。

lightbulb

解题思路

方法一：枚举

我们枚举所有可能的方向，对于每个方向 $(a, b)$ ，我们从 $(\textit{rMove}, \textit{cMove})$ 出发，用一个变量 $\textit{cnt}$ 记录我们走过的格子数，如果我们在走的过程中遇到了颜色为 $\textit{color}$ 的格子，且 $\textit{cnt} > 1$ ，那么我们就找到了一个好线段，返回 $\textit{true}$ 。

枚举结束后，如果我们没有找到任何好线段，那么返回 $\textit{false}$ 。

时间复杂度 $O(m + n)$ ，其中 $m$ 为 $\textit{board}$ 的行数，而 $n$ 为 $\textit{board}$ 的列数，本题中 $m = n = 8$ 。空间复杂度 $O(1)$ 。

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class Solution:
    def checkMove(
        self, board: List[List[str]], rMove: int, cMove: int, color: str
    ) -> bool:
        for a in range(-1, 2):
            for b in range(-1, 2):
                if a == 0 and b == 0:
                    continue
                i, j = rMove, cMove
                cnt = 0
                while 0 <= i + a < 8 and 0 <= j + b < 8:
                    cnt += 1
                    i, j = i + a, j + b
                    if cnt > 1 and board[i][j] == color:
                        return True
                    if board[i][j] in (color, "."):
                        break
        return False

speed

复杂度分析

指标	值
时间	complexity is O(1) since the board size is fixed at 8x8 and each direction has at most 7 cells to check. Space complexity is O(1) as only temporary variables are used for direction checks without extra structures.
空间	Depends on the final approach

psychology

面试官常问的追问

外企场景

question_mark
Asks if all eight directions are considered for a good line
question_mark
Wants reasoning on why a move is illegal even if it creates a middle line
question_mark
Checks understanding of endpoint vs middle cells in Array plus Matrix pattern

warning

常见陷阱

外企场景

error
Only checking one or two directions instead of all eight
error
Mistaking middle cell placement for endpoint legality
error
Not handling board boundaries correctly when scanning lines

swap_horiz

进阶变体

外企场景

arrow_right_alt
Check if multiple moves are legal in batch
arrow_right_alt
Support boards larger than 8x8 with same good line rules
arrow_right_alt
Determine all legal moves for a given color on the current board

help

常见问题

外企场景

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