19 February 2020, Unidentified flying object (UFO) has captured student’s attention on top of the CSE building of Sylhet Engineering College. The door of the UFO was closed. Students found a tiny LCD monitor on the door. It’s just displaying 2 strings on separate lines. Let’s call the strings p and q. Actually the passcode of the door is hidden in these two strings and length is minimal. The passcode is any string if and only if p and q are its subsequence. Example - let p = abcab & q = cba Accepted Passcodes of the door are -abcaba, abcbab, acbcab, cabcab.

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