I was interviewed by four people, and the questions were not hard. They included tasks such as replacing a character in a string and validating a BST.

I made a mistake which shouldn't have happened, but that interviewer was apparently not that smart. After I made that mistake, he became skeptical of everything I wrote on the board, even though the code was copied directly from the textbook.

Replace a character in a string with another one, or another two.

This operation involves substituting a character at a specific position within a string. You can replace a single character with another single character or with a sequence of two characters.