delete prdct;
Insert Into PRDCT Values (1,'A',to_date('01-May-2017'),to_date('31-dec-9999'));
Insert Into PRDCT Values (1,'B',to_date('01-Jun-2017'),to_date('31-dec-9999'));

with dates as ( 
  select distinct col, dt 
  from   prdct
  unpivot ( 
    dt for col in ( start_dt, end_dt )
  ) 
), ranges as (
  select col,
         dt start_dt, 
         lead ( dt ) over ( order by dt ) end_dt
  from   dates
), grps as (
  select distinct p.prdct_cd, p.id, d.start_dt, d.end_dt, col
  from   ranges d
  left join prdct p
  on     p.start_dt <= d.start_dt
  and    p.end_dt >= d.end_dt
), rws as (
  select g.*
  from   grps g
  where  end_dt is not null
), flags as (
  select col, id,
         start_dt, end_dt, 
         nvl ( a, 'N' ) a, 
         nvl ( b, 'N' ) b, 
         nvl ( c, 'N' ) c 
  from   rws 
  pivot (
    max ( case when prdct_cd is not null then 'Y' end )
    for  prdct_cd in ( 'A' a, 'B' b, 'C' c)
  )
)
  select col, id, 
         case 
           when col = 'END_DT' then start_dt + 1 
           else start_dt
         end start_dt, 
         case 
           when lead ( col ) over ( 
                  partition by id 
                  order by start_dt 
                ) = 'START_DT'
           then end_dt - 1
           else end_dt
         end end_dt, 
         a, b, c
  from   flags
  order  by start_dt;

COL        ID   START_DT               END_DT                 A   B   C   
START_DT      1 01-MAY-2017 00:00:00   31-MAY-2017 00:00:00   Y   N   N   
START_DT      1 01-JUN-2017 00:00:00   31-DEC-9999 00:00:00   Y   Y   N  

set serveroutput off
alter session set statistics_level = all;

<your query>

select * 
from   table(dbms_xplan.display_cursor(null, null, 'ALLSTATS LAST'));

update t
set    start_dt = date'2017-06-01'
where  prdct_cd = 'B';

select id,
    case when end_dt <= flag_a then 'Y' else 'N' end a_prod_ind,
    case when end_dt <= flag_b then 'Y' else 'N' end b_prod_ind,
    case when end_dt <= flag_c then 'Y' else 'N' end c_prod_ind,
    start_dt,end_dt
from (
select id,start_dt,end_dt,
    greatest( last_value( a_new_start_dt ignore nulls) over(order by end_dt rows between unbounded preceding and unbounded following) ,
    last_value( a_new_end_dt ignore nulls) over(order by end_dt rows between unbounded preceding and unbounded following) ) as flag_a ,
    greatest( last_value( b_new_start_dt ignore nulls) over(order by end_dt rows between unbounded preceding and unbounded following)  ,
    last_value( b_new_end_dt ignore nulls) over(order by end_dt rows between unbounded preceding and unbounded following) ) as flag_b ,
    greatest( last_value( c_new_start_dt ignore nulls) over(order by end_dt rows between unbounded preceding and unbounded following) ,
    last_value( c_new_end_dt ignore nulls) over(order by end_dt rows between unbounded preceding and unbounded following) ) as flag_c
from (
select *
from (
select t.*, start_dt x1,end_dt x2 from t
    )
pivot(
    max(x1) as new_start_dt,
    max(x2) as new_end_dt
    for prdct_cd in ('A' as a,'B' as b,'C' as c) )
      )
      )
/

ID A_PROD_IND  B_PROD_IND  C_PROD_IND   START_DT        END_DT                 
 1 Y           Y           Y            01-MAY-2017     31-JUL-2017 00:00:00    
 1 N           Y           Y            01-JUN-2017     31-AUG-2017 00:00:00    
 1 N           N           Y            01-MAY-2017     31-DEC-9999 00:00:00