Buggy python submission (verdict: Runtime Error):
import sys
import array
from itertools import accumulate
input = sys.stdin.readline
N,K = map(int,input().split())
xyc = []
for i in range(N):
    x,y,c = input().split()
    x = int(x)
    y = int(y)
    xyc.append([x % (2*K), y % (2*K), c])

wmap = [array.array('B',[0]*3*K) for i in [0]*3*K]
hmap = [array.array('B',[0]*3*K) for i in [0]*3*K]
for x,y,c in xyc:
    if c == 'W':
        wmap[y][x] += 1
        if y < K:
            wmap[y+2*K][x] += 1
        if x < K:
            wmap[y][x+2*K] += 1
        if x < K and y < K:
            wmap[y+2*K][x+2*K] += 1
    else:
        hmap[y][x] += 1
        if x < K:
            hmap[y][x+2*K] += 1
        if y < K:
            hmap[y+2*K][x] += 1
        if x < K and y < K:
            hmap[y+2*K][x+2*K] += 1

wcumsum = [array.array('I',[0]*(3*K+1))] + [array.array('I',[0]+list(accumulate(row))) for row in wmap]
hcumsum = [array.array('I',[0]*(3*K+1))] + [array.array('I',[0]+list(accumulate(row))) for row in hmap]

for y in range(1,3*K+1):
    for x in range(3*K+1):
        wcumsum[y][x] += wcumsum[y-1][x]
        hcumsum[y][x] += hcumsum[y-1][x]

def cs2(m, ltx, lty, rbx, rby):
    S = m[rby-1][rbx-1]
    S -= m[rby-1][ltx-1]
    S -= m[lty-1][rbx-1]
    S += m[lty-1][ltx-1]
    return S

ans = 0
for y in range(1,K+1):
    for x in range(1,K+1):
        ltw = cs2(wcumsum,x,y,x+K, y+K)
        rbw = cs2(wcumsum,x+K,y+K,x+2*K, y+2*K)
        lbh = cs2(hcumsum,x,y+K,x+K, y+2*K)
        rth = cs2(hcumsum,x+K,y,x+2*K, y+K)
        temp = ltw + rbw + lbh + rth
        ans = max(ans,temp)

        ltw = cs2(hcumsum,x,y,x+K, y+K)
        rbw = cs2(hcumsum,x+K,y+K,x+2*K, y+2*K)
        lbh = cs2(wcumsum,x,y+K,x+K, y+2*K)
        rth = cs2(wcumsum,x+K,y,x+2*K, y+K)
        temp = ltw + rbw + lbh + rth
        ans = max(ans,temp)

print(ans)
        



Fixed submission:
import sys
import array
input = sys.stdin.readline
N,K = map(int,input().split())
xyc = []
for i in range(N):
    x,y,c = input().split()
    x = int(x)
    y = int(y)
    xyc.append([x % (2*K), y % (2*K), c])

wmap = [array.array('I',[0]*3*K) for i in [0]*3*K]
hmap = [array.array('I',[0]*3*K) for i in [0]*3*K]
for x,y,c in xyc:
    if c == 'W':
        wmap[y][x] += 1
        if y < K:
            wmap[y+2*K][x] += 1
        if x < K:
            wmap[y][x+2*K] += 1
        if x < K and y < K:
            wmap[y+2*K][x+2*K] += 1
    else:
        hmap[y][x] += 1
        if x < K:
            hmap[y][x+2*K] += 1
        if y < K:
            hmap[y+2*K][x] += 1
        if x < K and y < K:
            hmap[y+2*K][x+2*K] += 1

def accum(L):
    res = [0]*(len(L)+1)
    res[1] = L[0]
    for i in range(2,len(L)+1):
        res[i] = res[i-1] + L[i-1]
    return res
wcumsum = [array.array('I',[0]*(3*K+1))] + [array.array('I',accum(row)) for row in wmap]
hcumsum = [array.array('I',[0]*(3*K+1))] + [array.array('I',accum(row)) for row in hmap]

for y in range(1,3*K+1):
    for x in range(3*K+1):
        wcumsum[y][x] += wcumsum[y-1][x]
        hcumsum[y][x] += hcumsum[y-1][x]

def cs2(m, ltx, lty, rbx, rby):
    S = m[rby-1][rbx-1]
    S -= m[rby-1][ltx-1]
    S -= m[lty-1][rbx-1]
    S += m[lty-1][ltx-1]
    return S

ans = 0
for y in range(1,K+1):
    for x in range(1,K+1):
        ltw = cs2(wcumsum,x,y,x+K, y+K)
        rbw = cs2(wcumsum,x+K,y+K,x+2*K, y+2*K)
        lbh = cs2(hcumsum,x,y+K,x+K, y+2*K)
        rth = cs2(hcumsum,x+K,y,x+2*K, y+K)
        temp = ltw + rbw + lbh + rth
        ans = max(ans,temp)

        ltw = cs2(hcumsum,x,y,x+K, y+K)
        rbw = cs2(hcumsum,x+K,y+K,x+2*K, y+2*K)
        lbh = cs2(wcumsum,x,y+K,x+K, y+2*K)
        rth = cs2(wcumsum,x+K,y,x+2*K, y+K)
        temp = ltw + rbw + lbh + rth
        ans = max(ans,temp)

print(ans)

Buggy python submission (verdict: Runtime Error):
import sys
import array
from itertools import accumulate
input = sys.stdin.readline
N,K = map(int,input().split())
xyc = []
for i in range(N):
    x,y,c = input().split()
    x = int(x)
    y = int(y)
    xyc.append([x % (2*K), y % (2*K), c])

wmap = [array.array('H',[0]*3*K) for i in [0]*3*K]
hmap = [array.array('H',[0]*3*K) for i in [0]*3*K]
for x,y,c in xyc:
    if c == 'W':
        wmap[y][x] += 1
        if y < K:
            wmap[y+2*K][x] += 1
        if x < K:
            wmap[y][x+2*K] += 1
        if x < K and y < K:
            wmap[y+2*K][x+2*K] += 1
    else:
        hmap[y][x] += 1
        if x < K:
            hmap[y][x+2*K] += 1
        if y < K:
            hmap[y+2*K][x] += 1
        if x < K and y < K:
            hmap[y+2*K][x+2*K] += 1

wcumsum = [array.array('H',[0]*(3*K+1))] + [array.array('H',[0]+list(accumulate(row))) for row in wmap]
hcumsum = [array.array('H',[0]*(3*K+1))] + [array.array('H',[0]+list(accumulate(row))) for row in hmap]

for y in range(1,3*K+1):
    for x in range(3*K+1):
        wcumsum[y][x] += wcumsum[y-1][x]
        hcumsum[y][x] += hcumsum[y-1][x]

def cs2(m, ltx, lty, rbx, rby):
    S = m[rby-1][rbx-1]
    S -= m[rby-1][ltx-1]
    S -= m[lty-1][rbx-1]
    S += m[lty-1][ltx-1]
    return S

ans = 0
for y in range(1,K+1):
    for x in range(1,K+1):
        ltw = cs2(wcumsum,x,y,x+K, y+K)
        rbw = cs2(wcumsum,x+K,y+K,x+2*K, y+2*K)
        lbh = cs2(hcumsum,x,y+K,x+K, y+2*K)
        rth = cs2(hcumsum,x+K,y,x+2*K, y+K)
        temp = ltw + rbw + lbh + rth
        ans = max(ans,temp)

        ltw = cs2(hcumsum,x,y,x+K, y+K)
        rbw = cs2(hcumsum,x+K,y+K,x+2*K, y+2*K)
        lbh = cs2(wcumsum,x,y+K,x+K, y+2*K)
        rth = cs2(wcumsum,x+K,y,x+2*K, y+K)
        temp = ltw + rbw + lbh + rth
        ans = max(ans,temp)

print(ans)
        



Fixed submission:
import sys
import array
input = sys.stdin.readline
N,K = map(int,input().split())
xyc = []
for i in range(N):
    x,y,c = input().split()
    x = int(x)
    y = int(y)
    xyc.append([x % (2*K), y % (2*K), c])

wmap = [array.array('I',[0]*3*K) for i in [0]*3*K]
hmap = [array.array('I',[0]*3*K) for i in [0]*3*K]
for x,y,c in xyc:
    if c == 'W':
        wmap[y][x] += 1
        if y < K:
            wmap[y+2*K][x] += 1
        if x < K:
            wmap[y][x+2*K] += 1
        if x < K and y < K:
            wmap[y+2*K][x+2*K] += 1
    else:
        hmap[y][x] += 1
        if x < K:
            hmap[y][x+2*K] += 1
        if y < K:
            hmap[y+2*K][x] += 1
        if x < K and y < K:
            hmap[y+2*K][x+2*K] += 1

def accum(L):
    res = [0]*(len(L)+1)
    res[1] = L[0]
    for i in range(2,len(L)+1):
        res[i] = res[i-1] + L[i-1]
    return res
wcumsum = [array.array('I',[0]*(3*K+1))] + [array.array('I',accum(row)) for row in wmap]
hcumsum = [array.array('I',[0]*(3*K+1))] + [array.array('I',accum(row)) for row in hmap]

for y in range(1,3*K+1):
    for x in range(3*K+1):
        wcumsum[y][x] += wcumsum[y-1][x]
        hcumsum[y][x] += hcumsum[y-1][x]

def cs2(m, ltx, lty, rbx, rby):
    S = m[rby-1][rbx-1]
    S -= m[rby-1][ltx-1]
    S -= m[lty-1][rbx-1]
    S += m[lty-1][ltx-1]
    return S

ans = 0
for y in range(1,K+1):
    for x in range(1,K+1):
        ltw = cs2(wcumsum,x,y,x+K, y+K)
        rbw = cs2(wcumsum,x+K,y+K,x+2*K, y+2*K)
        lbh = cs2(hcumsum,x,y+K,x+K, y+2*K)
        rth = cs2(hcumsum,x+K,y,x+2*K, y+K)
        temp = ltw + rbw + lbh + rth
        ans = max(ans,temp)

        ltw = cs2(hcumsum,x,y,x+K, y+K)
        rbw = cs2(hcumsum,x+K,y+K,x+2*K, y+2*K)
        lbh = cs2(wcumsum,x,y+K,x+K, y+2*K)
        rth = cs2(wcumsum,x+K,y,x+2*K, y+K)
        temp = ltw + rbw + lbh + rth
        ans = max(ans,temp)

print(ans)