Buggy python submission (verdict: Time Limit Exceeded):
import sys

import numpy as np

sys.setrecursionlimit(10000)
INF = float('inf')

N, K = map(int, next(sys.stdin).split())

MOD = K * 2
grid = np.zeros((MOD, MOD))


def draw(sx, sy, ex, ey):
    sx %= MOD
    sy %= MOD
    ex = (ex - 1) % MOD + 1
    ey = (ey - 1) % MOD + 1

    if sx < ex and sy < ey:
        grid[sx, sy] += 1
        if ex < MOD:
            grid[ex, sy] -= 1
        if ey < MOD:
            grid[sx, ey] -= 1
        if ex < MOD and ey < MOD:
            grid[ex, ey] += 1

    elif ex <= sx:
        if ey <= sy:
            draw(0, 0, ex, ey)
            draw(0, sy, ex, MOD)
            draw(sx, 0, MOD, ey)
            draw(sx, sy, MOD, MOD)
        else:
            draw(0, sy, ex, ey)
            draw(sx, sy, MOD, ey)
    else:
        draw(sx, 0, ex, ey)
        draw(sx, sy, ex, MOD)


for _ in range(N):
    x, y, c = next(sys.stdin).split()
    x = int(x)
    y = int(y)
    if c == 'W':
        x += K

    # 黒マスをどこに置けばこの条件を満たすか
    # 累積和とったときに条件を満たす範囲だけ +1 されるように調整
    draw(x, y, x + K, y + K)
    draw(x + K, y + K, x + K * 2, y + K * 2)
print(int(grid.cumsum(axis=0).cumsum(axis=1).max()))


Fixed submission:
import sys

sys.setrecursionlimit(10000)
INF = float('inf')

N, K = map(int, next(sys.stdin).split())

MOD = K * 2
grid = [[0 for _ in range(MOD)] for _ in range(MOD)]


def draw(sx, sy, ex, ey):
    sx %= MOD
    sy %= MOD
    ex = (ex - 1) % MOD + 1
    ey = (ey - 1) % MOD + 1

    if sx < ex and sy < ey:
        grid[sx][sy] += 1
        if ex < MOD:
            grid[ex][sy] -= 1
        if ey < MOD:
            grid[sx][ey] -= 1
        if ex < MOD and ey < MOD:
            grid[ex][ey] += 1

    elif ex <= sx:
        if ey <= sy:
            draw(0, 0, ex, ey)
            draw(0, sy, ex, MOD)
            draw(sx, 0, MOD, ey)
            draw(sx, sy, MOD, MOD)
        else:
            draw(0, sy, ex, ey)
            draw(sx, sy, MOD, ey)
    else:
        draw(sx, 0, ex, ey)
        draw(sx, sy, ex, MOD)


for _ in range(N):
    x, y, c = next(sys.stdin).split()
    x = int(x)
    y = int(y)
    if c == 'W':
        x += K

    # 黒マスをどこに置けばこの条件を満たすか
    # 累積和とったときに条件を満たす範囲だけ +1 されるように調整
    draw(x, y, x + K, y + K)
    draw(x + K, y + K, x + K * 2, y + K * 2)

for i in range(MOD - 1):
    for j in range(MOD):
        grid[i + 1][j] += grid[i][j]
for i in range(MOD - 1):
    for j in range(MOD):
        grid[j][i + 1] += grid[j][i]
ans = 0
for i in range(MOD):
    ans = max(ans, *grid[i])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import sys

import numpy as np

sys.setrecursionlimit(10000)
INF = float('inf')

N, K = list(map(int, input().split()))

MOD = K * 2
grid = np.zeros((MOD, MOD))


def draw(sx, sy, ex, ey):
    sx %= MOD
    sy %= MOD
    ex = (ex - 1) % MOD + 1
    ey = (ey - 1) % MOD + 1

    if sx < ex and sy < ey:
        grid[sx, sy] += 1
        if ex < MOD:
            grid[ex, sy] -= 1
        if ey < MOD:
            grid[sx, ey] -= 1
        if ex < MOD and ey < MOD:
            grid[ex, ey] += 1

    elif ex <= sx:
        if ey <= sy:
            draw(0, 0, ex, ey)
            draw(0, sy, ex, MOD)
            draw(sx, 0, MOD, ey)
            draw(sx, sy, MOD, MOD)
        else:
            draw(0, sy, ex, ey)
            draw(sx, sy, MOD, ey)
    else:
        draw(sx, 0, ex, ey)
        draw(sx, sy, ex, MOD)


for _ in range(N):
    x, y, c = input().split()
    x = int(x)
    y = int(y)
    if c == 'W':
        x += K

    # 黒マスをどこに置けばこの条件を満たすか
    # 累積和とったときに条件を満たす範囲だけ +1 されるように調整
    draw(x, y, x + K, y + K)
    draw(x + K, y + K, x + K * 2, y + K * 2)
print(int(grid.cumsum(axis=0).cumsum(axis=1).max()))


Fixed submission:
import sys

sys.setrecursionlimit(10000)
INF = float('inf')

N, K = map(int, next(sys.stdin).split())

MOD = K * 2
grid = [[0 for _ in range(MOD)] for _ in range(MOD)]


def draw(sx, sy, ex, ey):
    sx %= MOD
    sy %= MOD
    ex = (ex - 1) % MOD + 1
    ey = (ey - 1) % MOD + 1

    if sx < ex and sy < ey:
        grid[sx][sy] += 1
        if ex < MOD:
            grid[ex][sy] -= 1
        if ey < MOD:
            grid[sx][ey] -= 1
        if ex < MOD and ey < MOD:
            grid[ex][ey] += 1

    elif ex <= sx:
        if ey <= sy:
            draw(0, 0, ex, ey)
            draw(0, sy, ex, MOD)
            draw(sx, 0, MOD, ey)
            draw(sx, sy, MOD, MOD)
        else:
            draw(0, sy, ex, ey)
            draw(sx, sy, MOD, ey)
    else:
        draw(sx, 0, ex, ey)
        draw(sx, sy, ex, MOD)


for _ in range(N):
    x, y, c = next(sys.stdin).split()
    x = int(x)
    y = int(y)
    if c == 'W':
        x += K

    # 黒マスをどこに置けばこの条件を満たすか
    # 累積和とったときに条件を満たす範囲だけ +1 されるように調整
    draw(x, y, x + K, y + K)
    draw(x + K, y + K, x + K * 2, y + K * 2)

for i in range(MOD - 1):
    for j in range(MOD):
        grid[i + 1][j] += grid[i][j]
for i in range(MOD - 1):
    for j in range(MOD):
        grid[j][i + 1] += grid[j][i]
ans = 0
for i in range(MOD):
    ans = max(ans, *grid[i])
print(ans)