In Python:

I need help using depth first search to solve this euler problem: The text file"keylog.txt" is at :https://drive.google.com/file/d/0B23lG851VqEdVnNSWlJsZ2ZYbjA/view and contains 50 succesful logins. Thank you in advance.

A common security method used for online banking is to ask the user for three random characters from a passcode. For example, if the passcode was 531278, they may ask for the 2nd, 3rd, and 5th characters; the expected reply would be: 317. Given that the three characters are always asked for in order, analyse the file so as to determine the shortest possible secret passcode of unknown length