Step 1 : Find out the INCREMENT BY parameter for the sequence with the
following query: 
	Select INCREMENT_BY
	From   USER_SEQUENCES
	Where SEQUENCE_NAME = 'EMP_NO_SEQ' ;
This will return 1. It is not always necessary to run the above query tofind out the INCREMENT BY value. You 
can find it out by looking at the column data for which the sequence is used. 

Step 2 : Alter the sequence with a negative INCREMENT BY value: 
	alter sequence EMP_NO_SEQ increment by -1;

Step 3 : Run the PL/SQL block below to reset the 
sequence value to a desired number: 

	DECLARE
		TEMP   Number(10);
	BEGIN
		While(TRUE)
		LOOP
			Select  EMP_NO_SEQ.nextval
			Into     TEMP
			From   DUAL;
			IF ( TEMP = 100) THEN
			    Exit;
			END IF;
		END LOOP;
	EXCEPTION
		When Others Then
			Dbms_output.Put_line(SQLERRM);
	END;
Step 4 : Again reset the INCREMENT BY value to Original 
	alter sequence EMP_NO_SEQ increment by 1;

You can pack all this into One single stored procedure and use dynamic sql to alter the sequences.
Then Use DBMS_job to schedule it ( run it every day, so that the sequence is reset every day).