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，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' 。

/*
 * 思路：
 * 1. 使用Java Stream API进行同样的方向检查。
 * 2. 好线段的定义是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，并且线段上不能有任何空格子。
 */
import java.util.stream.IntStream;
public class Solution {
    public boolean checkMove(char[][] board, int rMove, int cMove, char color) {
        int[][] directions = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}, {1, 1}, {-1, -1}, {1, -1}, {-1, 1}};
        char opponent = color == 'B' ? 'W' : 'B';
        return IntStream.range(0, directions.length).anyMatch(i -> {
            int[] dir = directions[i];
            int r = rMove + dir[0];
            int c = cMove + dir[1];
            boolean seenOpponent = false;
            while (r >= 0 && r < 8 && c >= 0 && c < 8) {
                if (board[r][c] == '.') break;
                if (board[r][c] == opponent) {
                    seenOpponent = true;
                } else if (board[r][c] == color) {
                    return seenOpponent;
                }
                r += dir[0];
                c += dir[1];
            }
            return false;
        });
    }
}

题解的思路是在棋盘上模拟将选定的格子涂成指定颜色后，检查它是否成为一个好线段的端点。为此，代码首先模拟涂色，然后从该点向八个方向（上、下、左、右、四个对角线方向）检查。通过逐步扩展到下一个格子，代码寻找相同颜色的端点，同时确保中间没有空格，并且中间的格子颜色为另一种。如果在任何方向上找到至少三个格子组成的线段，且端点与初始颜色相同，则返回true，否则检查下一个方向。如果所有方向都不满足条件，则返回false。

O(1)

O(1)