# HackerRank 'Caesar Cipher' Solution

Martin Kysel · June 22, 2015

##### Short Problem Definition:

Julius Caesar protected his confidential information from his enemies by encrypting it. Caesar rotated every alphabet in the string by a fixed number K. This made the string unreadable by the enemy. You are given a string S and the number K. Encrypt the string and print the encrypted string.

Caesar Cipher

##### Complexity:

time complexity is `O(?)`

space complexity is `O(?)`

##### Execution:

This task has a few non-obvious pitfalls.

• upper case does not rotate into lower case (as one would expect from ascii)
• k can be bigger than the alphabet size (and must be corrected or a modulo operation on the whole sum must be performed)

Basically you need separate logic for upper case and lower case letters.

##### Solution:
``````
#!/usr/bin/py
def encryptCaesar(s, k):
output = list(s)
k %= (ord('z') - ord('a') + 1)

for idx, l in enumerate(output):
if l.isalpha():
if l.isupper():
new_char = ord(l)+k
if new_char > ord('Z'):
new_char = new_char - ord('Z') + ord('A') - 1
output[idx] = chr(new_char)
else:
new_char = ord(l)+k
if new_char > ord('z'):
new_char = new_char - ord('z') + ord('a') - 1
output[idx] = chr(new_char)
return ''.join(output)

if __name__ == '__main__':
n = input()
s = raw_input()
k = input()
print encryptCaesar(s, k)

``````