Codility ‘SqlSegmentsSum’ Kalium 2015 Solution

Short Problem Definition:

Compute the total length covered by 1-dimensional segments.

Link

SqlSegmentSum

Complexity:

time complexity

space complexity

Execution:

I first create a numbers table from 1 to 1.000.000, this could be done just once when creating the DB. In this challenge it adds a flat 0.3sec runtime to all testcases.

In the second step I simply unique join the segments and number tables.

Solution:
-- create numbers utility structure, very basic integer primary key column n
create table numbers(n integer not null, primary key(n asc));
-- insert generated sequential integers
insert into numbers(n)
select rowid
from (

-- build 1,000,000 rows using Cartesian product
select 1
from (
   select 0 union select 1 union select 2 union select 3
   union select 4 union select 5 union select 6
   union select 7 union select 8 union select 9
) a, (
   select 0 union select 1 union select 2 union select 3
   union select 4 union select 5 union select 6
   union select 7 union select 8 union select 9
) b, (
   select 0 union select 1 union select 2 union select 3
   union select 4 union select 5 union select 6
   union select 7 union select 8 union select 9
) c, (
   select 0 union select 1 union select 2 union select 3
   union select 4 union select 5 union select 6
   union select 7 union select 8 union select 9
) d, (
   select 0 union select 1 union select 2 union select 3
   union select 4 union select 5 union select 6
   union select 7 union select 8 union select 9
) e, (
   select 0 union select 1 union select 2 union select 3
   union select 4 union select 5 union select 6
   union select 7 union select 8 union select 9
) f

) derived;

select count(distinct n) from numbers inner join segments
on numbers.n between segments.l+1 and segments.r

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