I passed two OAs and got two rounds of phone interviews. The OAs were quite classical, but the phone interviews were quite different from the ones I've attended before. The interviewer used to post the questions beforehand, but this time, I needed to type all the conditions and variables we discussed during the interview onto the screen.

if function(s1) == function(s2) return true else return false

if encounter target character for example 'b', then delete one character before it. Otherwise, no operation is needed. When there are too many 'b's, return "".

For example:

accc => accc accb => ac abdd => dd