Advent of Code — Day 4

Published in

Microsoft Azure

3 min readDec 5, 2022

Day 4 — Camp Cleanup challenge is all about dealing with intervals. Intervals are trickier and more complex than one might think. No surprise the organizer of the Advent Of Code, included them in their challenges.

I did a lot of research on intervals, and specifically time intervals in the past, with a specific focus on how they can be applied to Business Intelligence and more specifically to Fact Table. Couple of slide decks I created lately on the subject are the following:

As usual I’m importing the input data and storing it into a table. Input data contains pairs of intervals, so I’m splitting the pairs and the interval begin and end into dedicated columns, for easier manipulation:

create table dbo.ch04_input 
(
    id int identity not null primary key,
    pair1_b int,
    pair1_e int,
    pair2_b int,
    pair2_e int
);

with cteLines as
(
    select 
        trim(replace([value], char(13), '')) as [line]
    from
        string_split(@input, char(10))
),
ctePairs as
(
    select 
        left([line], charindex(',', [line])-1) as pair1,
        right([line], len([line]) - charindex(',', [line])) as pair2
    from
        cteLines
)
insert into 
    dbo.ch04_input (pair1_b, pair1_e, pair2_b, pair2_e)
select
    left([pair1], charindex('-', [pair1])-1)  as pair1_b,
    right([pair1], len([pair1]) - charindex('-', [pair1])) as pair1_e,
    left([pair2], charindex('-', [pair2])-1) as pair2_b,
    right([pair2], len([pair2]) - charindex('-', [pair2])) as pair2_e
from
    ctePairs

the result is the following:

Part 1

The challenges ask to find all the pairs where one interval is completely included in the other. We must use the CONTAINS operator that can be expressed using simple math:

the query, therefore, is:

select
    count(*) 
from 
    ch04_input
where
    (pair1_b >= pair2_b and pair1_e <= pair2_e) -- pair1 CONTAINS pair2
or
    (pair2_b >= pair1_b and pair2_e <= pair1_e) -- pair2 CONTAINS pair1

Challenge solved.

Part 2

The second challenge requires to find all the pairs in which interval overlaps. There’s an operator for that, and the math is even simpler:

The query then is:

select
    count(*)
from 
    ch04_input a
where
    (pair1_b <= pair2_e and pair2_b <= pair1_e) -- OVERLAPS

Challenge completed.

Advent of Code — Day 4

Part 1

Part 2

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Written by Davide Mauri