def encode(message, rails):

message=message.replace(' ','')

encoded=''

next=0

for i in range(rails):

if i in [0,rails-1]:

suffix=rails*2-2

while next<len(message):

encoded+=message[next]

next+=suffix

next=i+1

else:

next=i

down=True

while next<len(message):

encoded+=message[next]

if down:

suffix=rails*2-2-2*i

else:

suffix=2*i

next+=suffix

down= not down

next=i+1

return encoded

def decode(encoded_message, rails):

#calculate the length of rails

length=[]

for i in range(rails):

if i==0:

length.append(len(encoded_message)//(2*rails-2))

elif i==rails-1:

length.append(length[0])

else:

length.append(length[0]*2)

remainder=len(encoded_message)%(2*rails-2)

down=True

i=0

while remainder>0:

length[i]+=1

remainder-=1

if down:

i+=1

else:

i-=1

if i==len(length)-1:

down=not down

#creating rails based on length

start=0

rail_list=[]

for width in length:

rail_list.append(list(encoded_message[start:start+width]))

start+=width

#decrypting the message from rails

down=True

decoded=''

i=0

while True:

decoded+=rail_list[i][0]

del(rail_list[i][0])

if i==0:

down=True

elif i==rails-1:

down=False

if down:

i+=1

else:

i-=1

#checking if entire message is decoded

is_empty=False

count=0

for j in range(rails):

if len(rail_list[j])==0:

count+=1

if count==rails:

is_empty=True

break

else:

break

if is_empty:

break

return decoded