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

read=sys.stdin.read
readline=sys.stdin.readline

def main():
  wb={'W':0,'B':1}
  n,k=map(int,readline().split())
  xyc=[l.split() for l in read().splitlines()]
  xyc=[[int(lst[0]) % (2*k),int(lst[1]) % (2*k),wb[lst[2]]] for lst in xyc]
  mat=np.zeros((2,4*k+1,4*k+1),dtype='int64')
  cand=np.zeros((2*k+1,2*k+1),dtype='int64')
  for i in range(4):
    for x,y,c in xyc:
      mat[c,:x+2+2*k*(i&1),:y+2+2*k*(i>>1&1)]+=1
  cand=mat[0,k:3*k+1,k:3*k+1]+mat[0,:2*k+1,:2*k+1]-mat[0,k:3*k+1,:2*k+1]-mat[0,:2*k+1,k:3*k+1]\
      +mat[0,2*k:4*k+1,2*k:4*k+1]+mat[0,k:3*k+1,k:3*k+1]-mat[0,2*k:4*k+1,k:3*k+1]-mat[0,k:3*k+1,2*k:4*k+1]\
      +mat[1,2*k:4*k+1,k:3*k+1]+mat[1,k:3*k+1,:2*k+1]-mat[1,2*k:4*k+1,:2*k+1]-mat[1,k:3*k+1,k:3*k+1]\
      +mat[1,k:3*k+1,2*k:4*k+1]+mat[1,:2*k+1,k:3*k+1]-mat[1,:2*k+1,2*k:4*k+1]-mat[1,k:3*k+1,k:3*k+1]
  print(np.max(cand))
  
if __name__=='__main__':
  main()
  
  
  


Fixed submission:
import sys
import numpy as np

read=sys.stdin.read
readline=sys.stdin.readline

def main():
  wb={'W':1,'B':0}
  n,k=map(int,readline().split())
  xyc=[l.split() for l in read().splitlines()]
  xy=[[int(lst[0]) % (2*k),(int(lst[1])+k*wb[lst[2]]) % (2*k)] for lst in xyc]
  mat=np.zeros((k+1,2*k+1),dtype='int64')
  cand=np.zeros((k+1,k+1),dtype='int64')
  for e in xy:
    f0=e[0]>=k
    f1=e[1]>=k
    mat[e[0]-f0*k+1,e[1]+(-1)**f1*f0*k+1]+=1
  mat=np.cumsum(mat,axis=0)
  mat=np.cumsum(mat,axis=1)
  cand=mat[k,2*k]-mat[k,k:2*k+1]+mat[k,:k+1]\
       -np.reshape(mat[:k+1,2*k],(k+1,1))+2*mat[:,k:2*k+1]-2*mat[:,:k+1]
  print(max(np.max(cand),mat[k,2*k]-np.min(cand)))
  
if __name__=='__main__':
  main()

Buggy python submission (verdict: Runtime Error):
import sys
import numpy as np

read=sys.stdin.read
readline=sys.stdin.readline

def main():
  def mycount(x1,y1,x2,y2,mat,s):
    return mat[s,x2,y2]-mat[s,x1,y2]-mat[s,x2,y1]+mat[s,x1,y1]
  wb={'W':0,'B':1}
  n,k=map(int,readline().split())
  xyc=[l.split() for l in read().splitlines()]
  xyc=[[int(lst[0]) % (2*k),int(lst[1]) % (2*k),wb[lst[2]]] for lst in xyc]
  mat=np.zeros((2,4*k+1,4*k+1),dtype='int64')
  cand=np.zeros((2,2*k+1,2*k+1),dtype='int64')
  for i in range(4):
    for e in xyc:
      mat[e[2],e[0]+1+2*k*(i&1),e[1]+1+2*k*(i>>1&1)]+=1
  mat=np.cumsum(mat,axis=1)
  mat=np.cumsum(mat,axis=2)
 # for i in range(1,4*k+1):
 #   for j in range(1,4*k+1):
 #     mat[:,i,j]=mat[:,i,j]+mat[:,i-1,j]+mat[:,i,j-1]-mat[:,i-1,j-1]
  cand+=mat[0,k:3*k+1,k:3*k+1]+mat[0,:2*k+1,:2*k+1]-mat[0,k:3*k+1,:2*k+1]-mat[0,:2*k+1,k:3*k+1]\
  cand+=mat[0,2*k:4*k+1,2*k:4*k+1]+mat[0,k:3*k+1,k:3*k+1]-mat[0,2*k:4*k+1,k:3*k+1]-mat[0,k:3*k+1,2*k:4*k+1]\
  cand+=mat[1,2*k:4*k+1,k:3*k+1]+mat[1,k:3*k+1,:2*k+1]-mat[1,2*k:4*k+1,:2*k+1]-mat[1,k:3*k+1,k:3*k+1]\
  cand+=mat[1,k:3*k+1,2*k:4*k+1]+mat[1,:2*k+1,k:3*k+1]-mat[1,:2*k+1,2*k:4*k+1]-mat[1,k:3*k+1,k:3*k+1]
  #print(mat)
  print(np.max(cand))
  
if __name__=='__main__':
  main()
  
  
  


Fixed submission:
import sys
import numpy as np

read=sys.stdin.read
readline=sys.stdin.readline

def main():
  wb={'W':1,'B':0}
  n,k=map(int,readline().split())
  xyc=[l.split() for l in read().splitlines()]
  xy=[[int(lst[0]) % (2*k),(int(lst[1])+k*wb[lst[2]]) % (2*k)] for lst in xyc]
  mat=np.zeros((k+1,2*k+1),dtype='int64')
  cand=np.zeros((k+1,k+1),dtype='int64')
  for e in xy:
    f0=e[0]>=k
    f1=e[1]>=k
    mat[e[0]-f0*k+1,e[1]+(-1)**f1*f0*k+1]+=1
  mat=np.cumsum(mat,axis=0)
  mat=np.cumsum(mat,axis=1)
  cand=mat[k,2*k]-mat[k,k:2*k+1]+mat[k,:k+1]\
       -np.reshape(mat[:k+1,2*k],(k+1,1))+2*mat[:,k:2*k+1]-2*mat[:,:k+1]
  print(max(np.max(cand),mat[k,2*k]-np.min(cand)))
  
if __name__=='__main__':
  main()