If one of S [ i ] or S [ N - i - 1 ] is equal to ' ? ' , replace it with corresponding character
if ( S [ i ] == ' ? ' and S [ N - i - 1 ] != ' ? ' ) : NEW_LINE INDENT S [ i ] = S [ N - i - 1 ] NEW_LINE DEDENT elif ( S [ i ] != ' ? ' and S [ N - i - 1 ] == ' ? ' ) : NEW_LINE INDENT S [ N - i - 1 ] = S [ i ] NEW_LINE DEDENT