Buggy python submission (verdict: Time Limit Exceeded):
def imos2d(x1, y1, x2, y2, board):
    board[y1][x1] += 1
    board[y2][x2] += 1
    board[y2][x1] -= 1
    board[y1][x2] -= 1


if __name__ == '__main__':
    N, K = map(int, input().split())
    lines = [input() for _ in range(N)]

    # N, K = 4, 3
    # lines = ["0 1 W", "1 2 W", "5 3 B", "5 4 B"]

    K2 = 2 * K
    add_dict = {"W": 0, "B": K}
    board = [[0 for _ in range(K2 + 1)] for _ in range(K2 + 1)]
    for line in lines:
        ls = line.split()
        x = int(ls[0]) % K2
        y = (int(ls[1]) + add_dict[ls[2]]) % K2

        if (x < K and y < K) or (K <= x and K <= y):
            # 左上・右上・中央・左下・右下

            x_ = x % K
            y_ = y % K

            # 左上
            imos2d(0, 0, x_ + 1, y_ + 1, board)
            # 右上
            imos2d(x_ + K + 1, 0, K2, y_ + 1, board)
            # 左下
            imos2d(0, y_ + K + 1, x_ + 1, K2, board)
            # 右下
            imos2d(x_ + K + 1, y_ + K + 1, K2, K2, board)
            # 中央
            imos2d(x_ + 1, y_ + 1, x_ + K + 1, y_ + K + 1, board)
        else:
            # 上・下・左・右
            x_ = x % K
            y_ = y % K

            # 上
            imos2d(x_ + 1, 0, x_ + K + 1, y_ + 1, board)
            # 下
            imos2d(x_ + 1, y_ + K + 1, x_ + K + 1, K2, board)

            # 左
            imos2d(0, y_ + 1, x_ + 1, y_ + K + 1, board)
            imos2d(x_ + K + 1, y_ + 1, K2, y_ + K + 1, board)

    for y in range(K2):
        for x in range(K2):
            board[y][x + 1] += board[y][x]

    for y in range(K2):
        for x in range(K2):
            board[y + 1][x] += board[y][x]

    answer = 0
    for y in range(K2 + 1):
        for x in range(K2 + 1):
            answer = max(answer, board[y][x])

    print(answer)


Fixed submission:
import numpy as np


def imos2d(x1, y1, x2, y2, board):
    board[y1][x1] += 1
    board[y2][x2] += 1
    board[y2][x1] -= 1
    board[y1][x2] -= 1


if __name__ == '__main__':
    N, K = map(int, input().split())
    lines = [input() for _ in range(N)]

    # N, K = 4, 3
    # lines = ["0 1 W", "1 2 W", "5 3 B", "5 4 B"]

    K2 = 2 * K
    add_dict = {"W": 0, "B": K}
    board = [[0 for _ in range(K2 + 1)] for _ in range(K2 + 1)]
    for line in lines:
        ls = line.split()
        x = int(ls[0]) % K2
        y = (int(ls[1]) + add_dict[ls[2]]) % K2
        x_ = x % K
        y_ = y % K

        # 左上・右上・中央・左下・右下
        if (x < K and y < K) or (K <= x and K <= y):
            # 左上
            imos2d(0, 0, x_ + 1, y_ + 1, board)
            # 右上
            imos2d(x_ + K + 1, 0, K2, y_ + 1, board)
            # 左下
            imos2d(0, y_ + K + 1, x_ + 1, K2, board)
            # 右下
            imos2d(x_ + K + 1, y_ + K + 1, K2, K2, board)
            # 中央
            imos2d(x_ + 1, y_ + 1, x_ + K + 1, y_ + K + 1, board)
        # 上・下・左・右
        else:
            # 上
            imos2d(x_ + 1, 0, x_ + K + 1, y_ + 1, board)
            # 下
            imos2d(x_ + 1, y_ + K + 1, x_ + K + 1, K2, board)

            # 左
            imos2d(0, y_ + 1, x_ + 1, y_ + K + 1, board)
            imos2d(x_ + K + 1, y_ + 1, K2, y_ + K + 1, board)

    board = np.array(board)
    for x in range(K2):
        board[:, x + 1] += board[:, x]
    for y in range(K2):
        board[y + 1, :] += board[y, :]

    print(board.max())

Buggy python submission (verdict: Time Limit Exceeded):
def imos2d(x1, y1, x2, y2, board):
    board[y1][x1] += 1
    board[y2][x2] += 1
    board[y2][x1] -= 1
    board[y1][x2] -= 1


if __name__ == '__main__':
    N, K = map(int, input().split())
    lines = [input() for _ in range(N)]

    # N, K = 4, 3
    # lines = ["0 1 W", "1 2 W", "5 3 B", "5 4 B"]

    K2 = 2 * K
    add_dict = {"W": 0, "B": K}
    board = [[0 for _ in range(K2 + 1)] for _ in range(K2 + 1)]
    for line in lines:
        ls = line.split()
        x = int(ls[0]) % K2
        y = (int(ls[1]) + add_dict[ls[2]]) % K2

        if (x < K and y < K) or (K <= x and K <= y):
            # 左上・右上・中央・左下・右下

            x_ = x % K
            y_ = y % K

            # 左上
            imos2d(0, 0, x_ + 1, y_ + 1, board)
            # 右上
            imos2d(x_ + K + 1, 0, K2, y_ + 1, board)
            # 左下
            imos2d(0, y_ + K + 1, x_ + 1, K2, board)
            # 右下
            imos2d(x_ + K + 1, y_ + K + 1, K2, K2, board)
            # 中央
            imos2d(x_ + 1, y_ + 1, x_ + K + 1, y_ + K + 1, board)
        else:
            # 上・下・左・右
            x_ = x % K
            y_ = y % K

            # 上
            imos2d(x_ + 1, 0, x_ + K + 1, y_ + 1, board)
            # 下
            imos2d(x_ + 1, y_ + K + 1, x_ + K + 1, K2, board)

            # 左
            imos2d(0, y_ + 1, x_ + 1, y_ + K + 1, board)
            imos2d(x_ + K + 1, y_ + 1, K2, y_ + K + 1, board)

    answer = 0
    for y in range(K2):
        for x in range(K2):
            board[y][x + 1] += board[y][x]
            answer = max(answer, board[y][x + 1])

    for y in range(K2):
        for x in range(K2):
            board[y + 1][x] += board[y][x]
            answer = max(answer, board[y + 1][x])

    print(answer)


Fixed submission:
import numpy as np


def imos2d(x1, y1, x2, y2, board):
    board[y1][x1] += 1
    board[y2][x2] += 1
    board[y2][x1] -= 1
    board[y1][x2] -= 1


if __name__ == '__main__':
    N, K = map(int, input().split())
    lines = [input() for _ in range(N)]

    # N, K = 4, 3
    # lines = ["0 1 W", "1 2 W", "5 3 B", "5 4 B"]

    K2 = 2 * K
    add_dict = {"W": 0, "B": K}
    board = [[0 for _ in range(K2 + 1)] for _ in range(K2 + 1)]
    for line in lines:
        ls = line.split()
        x = int(ls[0]) % K2
        y = (int(ls[1]) + add_dict[ls[2]]) % K2
        x_ = x % K
        y_ = y % K

        # 左上・右上・中央・左下・右下
        if (x < K and y < K) or (K <= x and K <= y):
            # 左上
            imos2d(0, 0, x_ + 1, y_ + 1, board)
            # 右上
            imos2d(x_ + K + 1, 0, K2, y_ + 1, board)
            # 左下
            imos2d(0, y_ + K + 1, x_ + 1, K2, board)
            # 右下
            imos2d(x_ + K + 1, y_ + K + 1, K2, K2, board)
            # 中央
            imos2d(x_ + 1, y_ + 1, x_ + K + 1, y_ + K + 1, board)
        # 上・下・左・右
        else:
            # 上
            imos2d(x_ + 1, 0, x_ + K + 1, y_ + 1, board)
            # 下
            imos2d(x_ + 1, y_ + K + 1, x_ + K + 1, K2, board)

            # 左
            imos2d(0, y_ + 1, x_ + 1, y_ + K + 1, board)
            imos2d(x_ + K + 1, y_ + 1, K2, y_ + K + 1, board)

    board = np.array(board)
    for x in range(K2):
        board[:, x + 1] += board[:, x]
    for y in range(K2):
        board[y + 1, :] += board[y, :]

    print(board.max())

Buggy python submission (verdict: Time Limit Exceeded):
import numpy as np


def imos2d(x1, y1, x2, y2, board):
    board[y1][x1] += 1
    board[y2][x2] += 1
    board[y2][x1] -= 1
    board[y1][x2] -= 1


if __name__ == '__main__':
    N, K = map(int, input().split())
    lines = [input().split() for _ in range(N)]
    xs, ys, cs = zip(*[[int(line[0]), int(line[1]), line[2]] for line in lines])

    # N, K = 4, 3
    # xs = [0, 1, 5, 5]
    # ys = [1, 2, 3, 4]
    # cs = ["W", "W", "B", "B"]

    K2 = 2 * K
    add_dict = {"W": 0, "B": K}
    board = np.zeros((K2 + 1, K2 + 1), np.int64)
    for x, y, c in zip(xs, ys, cs):
        x = x % K2
        y = (y + add_dict[c]) % K2

        if (x < K and y < K) or (K <= x and K <= y):
            # 左上・右上・中央・左下・右下

            x_ = x % K
            y_ = y % K

            # 左上
            imos2d(0, 0, x_ + 1, y_ + 1, board)
            # 右上
            imos2d(x_ + K + 1, 0, K2, y_ + 1, board)
            # 左下
            imos2d(0, y_ + K + 1, x_ + 1, K2, board)
            # 右下
            imos2d(x_ + K + 1, y_ + K + 1, K2, K2, board)
            # 中央
            imos2d(x_ + 1, y_ + 1, x_ + K + 1, y_ + K + 1, board)
        else:
            # 上・下・左・右
            x_ = x % K
            y_ = y % K

            # 上
            imos2d(x_ + 1, 0, x_ + K + 1, y_ + 1, board)
            # 下
            imos2d(x_ + 1, y_ + K + 1, x_ + K + 1, K2, board)

            # 左
            imos2d(0, y_ + 1, x_ + 1, y_ + K + 1, board)
            imos2d(x_ + K + 1, y_ + 1, K2, y_ + K + 1, board)

    board_cum = board.cumsum(axis=0).cumsum(axis=1)
    print(board_cum.max())


Fixed submission:
import numpy as np


def imos2d(x1, y1, x2, y2, board):
    board[y1][x1] += 1
    board[y2][x2] += 1
    board[y2][x1] -= 1
    board[y1][x2] -= 1


if __name__ == '__main__':
    N, K = map(int, input().split())
    lines = [input() for _ in range(N)]

    # N, K = 4, 3
    # lines = ["0 1 W", "1 2 W", "5 3 B", "5 4 B"]

    K2 = 2 * K
    add_dict = {"W": 0, "B": K}
    board = [[0 for _ in range(K2 + 1)] for _ in range(K2 + 1)]
    for line in lines:
        ls = line.split()
        x = int(ls[0]) % K2
        y = (int(ls[1]) + add_dict[ls[2]]) % K2
        x_ = x % K
        y_ = y % K

        # 左上・右上・中央・左下・右下
        if (x < K and y < K) or (K <= x and K <= y):
            # 左上
            imos2d(0, 0, x_ + 1, y_ + 1, board)
            # 右上
            imos2d(x_ + K + 1, 0, K2, y_ + 1, board)
            # 左下
            imos2d(0, y_ + K + 1, x_ + 1, K2, board)
            # 右下
            imos2d(x_ + K + 1, y_ + K + 1, K2, K2, board)
            # 中央
            imos2d(x_ + 1, y_ + 1, x_ + K + 1, y_ + K + 1, board)
        # 上・下・左・右
        else:
            # 上
            imos2d(x_ + 1, 0, x_ + K + 1, y_ + 1, board)
            # 下
            imos2d(x_ + 1, y_ + K + 1, x_ + K + 1, K2, board)

            # 左
            imos2d(0, y_ + 1, x_ + 1, y_ + K + 1, board)
            imos2d(x_ + K + 1, y_ + 1, K2, y_ + K + 1, board)

    board = np.array(board)
    for x in range(K2):
        board[:, x + 1] += board[:, x]
    for y in range(K2):
        board[y + 1, :] += board[y, :]

    print(board.max())