4. Write an algorithm to determine whether an input character string is of the form x C y where x is a string consisting only of the letters A and B and y is the reverse of the x (i.e. if x=ABABBA then y must equal ABBABA). At each point you may read only the next character in the string, i.e. you must process the string on a left to right basis. You may not use string functions.

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