Roughly 15 to 20 minutes, reading time inclusive
You are required to make a substitution cipher solver which solves the key of a given substitution cipher, assuming you don't know the uncrypted text, in reasonable time.
In cryptography, a substitution cipher is a one-to-one translation of characters a-z for an unencrypted text, where the translation mapping is specified by a key.
For example, if the key is "phqgiumeaylnofdxjkrcvstzwb", it means "a"->"p", "b"->"h", and so on.
Unencrypted text: defend the east wall of the castle
Encrypted text: giuifg cei iprc tpnn du cei qprcni
Clone the materials needed for the exercise at:
https://github.com/laichunpongben/coding-interview
In decrypted.txt. When you solve the problem, you assume you don't know this. For your reference only.
In encrypted.txt. This is after applying the cipher.
In vocab.txt. These are the words which come from the uncrypted text, sorted by alphabetical order and delimited by whitespace.
In descending significance:
- How you approach and solve the problem. Even psuedo-code or skeleton code can be material.
- Coding style
- Interaction with the peer (that's the interviewer, if any)
- Level of completion. However, don't feel discouraged if you cannot finish the solver.
- Use your own PC (or interviewer's PC), and your choice of programming language and development environment.
- Get help from googling/stackoverflow etc. But please don't directly search for "How to make a substitution cipher" or copy codes from GitHub etc. Remember, the purpose of this exercise is to evaluate YOUR skills.
- Discuss with the interviewer, if any. Think aloud may help.
- Ask the interviewer to shut up/leave, if you find him/her disturbing.
- Ask for wifi access, if necessary
Good luck and happy coding!