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Update README with hints about efficient solution

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Chris Hapgood
2024-06-11 09:12:30 -04:00
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README.md
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### The Sun Tribe Code Challenge
You are challenged to implement a date-interval difference function. The arguments to the function `difference` will be clojure sets, each
of which contains zero or more [LocalDateRange](https://www.threeten.org/threeten-extra/apidocs/org.threeten.extra/org/threeten/extra/LocalDateRange.html)
objects. The function must return a set of LocalDateRange objects that represents the [interval difference](http://mathinschool.com/page/8.html) of the
first set and all additional input sets.
objects. The function must return the minimal set of LocalDateRange objects that represents the [interval difference](http://mathinschool.com/page/8.html)
between the first set and all additional input sets.
For example, given a set containing the single data range representing the month of January 2024 and a second set containing a date range
representing the second week of January 2024 and a date range representing the single day of New Year's Day 2024, the function should return
@@ -14,10 +14,10 @@ Stated using algebraic symbols and leveraging the ISO representation of date int
```
### Context
At Sun Tribe Trading we gather the energy production data of solar generators from various sources (typically APIs from the manufacturers
of solar energy equipment) and submit the data to regulatory authorities. It's important that we accurately determine the energy data we need
to gather based on the data we already have on hand and the current reporting period. Date interval operations are central to this
computation.
At Sun Tribe Trading we gather the energy production data of solar generators from various sources (typically APIs provided by the
manufacturers of solar energy equipment) and submit the data to regulatory authorities. We must accurately determine the energy data
we need to gather based on the data we already have on hand and the current reporting period. Date interval operations are
central to this computation.
### Evaluation
Your solution will be evaluated as follows, in decreasing order of importance:
@@ -29,18 +29,21 @@ Correctness and performance will be evaluated by running this command in the roo
`time clojure -X:test`
Readability will be evaluated by your potential future colleagues looking at the entire contents of the repository. You may organize
the code of your implementation in any way you deem appropriate, but you must not modify the `challenge-test` namespace. You may
add additional tests in separate namespaces. You may introduce additional dependencies and make other modifications to the `deps.edn`
file, but you must not modify the `:test` alias.
Readability will be evaluated by your potential future colleagues looking at the entire contents of the repository.
You may organize the code of your implementation in any way you deem appropriate, but you must not modify the `challenge-test` namespace.
You may add additional tests in separate namespaces. You may introduce additional dependencies and make other modifications to the
`deps.edn` file, but you must not modify the `:test` alias.
### Scale of the Challenge
We believe that a performance-optimized solution to the problem is difficult and we have not attempted to implement it. We have
implemented a correct solution in less than fifty lines of documented Clojure code with no additional dependencies. It takes ~15 seconds
to complete the test suite on a 2023 MacBook Pro with an Apple M2 Pro processor and 32G of RAM.
A performance-optimized solution to the problem is difficult. We have implemented a correct solution in less than fifty lines of
documented Clojure code with no additional dependencies but leveraging many capabilities of the underlying `org.threeten.extra/LocalDateRange`
class. It takes about 15 seconds to complete the test suite on a 2023 MacBook Pro with an Apple M2 Pro processor and 32G of RAM. We have
also implemented an efficient solution in less then seventy lines of documented Clojure code with no additional dependencies. It takes
about two seconds to complete the test suite on the same machine; most of that time is spent loading Clojure itself.
### Hints, maybe helpful
Our solution evolved from the observation that a LocalDateRange object can be represented (inefficiently) by a sequence of
Our simple solution evolved from the observation that a LocalDateRange object can be represented (inefficiently) by a sequence of
[LocalDate](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/time/LocalDate.html) objects. That representation can be
input into a set difference operation, but the result must be "compressed" back into the minimal set of LocalDateRange
objects.
@@ -51,6 +54,10 @@ Before coding, you should be comfortable with the concept of a [time interval](h
more specifically a (local) date interval as implemented by
the [backing Java library we use](https://www.threeten.org/threeten-extra/apidocs/org.threeten.extra/org/threeten/extra/LocalDateRange.html).
Our efficient solution uses the properties of mathematical intervals (not necessarily date intervals). Consequently, the first and last
operations in this solution convert from LocalDateRange objects to Clojure data and from Clojure data back to LocalDateRange objects,
respectively. The necessary computational complexity of this alogrithm is high and the code reflects it.
### Submitting your response
This git repository is the entire input you will need for the Sun Tribe code challenge. Your submission should be a modified version
of this repository (including our initial commits and the commit(s) of your solution). You may submit either: