Advent of Code 2022, Day 1 - Part One

Preface

Now that we have the following data structure from our previous post, we start implementing the business logic to retrieve the highest combined number of calories.

[
  [ 1000, 2000, 3000 ], // Elve one
  [ 4000 ],             // Elve two
  [ 5000, 6000 ],       // Elve three
  [ 7000, 8000, 9000 ], // Elve four
  [ 10000 ]             // Elve five
]

Design

The objective of the first part of the assignment is to retrieve the highest amount of combined calories a single elve is carrying. So we need to sum up all the calories in each list from our data structure and get the biggest number.

flowchart LR
  subgraph eone["Elve one"]
    direction TB
    ae1["1000"]
    be1["2000"]
    ce1["3000"]

    ae1 ~~~ be1
    be1 ~~~ ce1
  end

  subgraph eonetotal["Elve one"]
    te1["Total: 5000"]
  end

  eone -- "Count calories" --- eonetotal

  subgraph etwo["Elve two"]
    ae2["4000"]
  end

  subgraph etwototal["Elve two"]
    te2["Total: 4000"]
  end

  etwo -- "Count calories" --- etwototal

  subgraph ethree["Elve three"]
    direction TB
    ae3["5000"]
    be3["6000"]

    ae3 ~~~ be3
  end

  subgraph ethreetotal["Elve three"]
    te3["Total: 11000"]
  end

  ethree -- "Count calories" --- ethreetotal

  subgraph efour["Elve four"]
    direction TB
    ae4["7000"]
    be4["8000"]
    ce4["9000"]

    ae4 ~~~ be4
    be4 ~~~ ce4
  end

  subgraph efourtotal["Elve four"]
    te4["Total: 24000"]
  end

  efour -- "Count calories" --- efourtotal

  subgraph efive["Elve five"]
    ae5["10000"]
  end

  subgraph efivetotal["Elve five"]
    te5["Total: 10000"]
  end

  efive -- "Count calories" --- efivetotal

  max["Max()"]
  biggest["Biggest number: <b>24000</b>"]

  eonetotal --> max
  etwototal --> max
  ethreetotal --> max
  efourtotal --> max
  efivetotal --> max

  max --> biggest

Implementation

Business logic

Now we know what we want our code to do, let’s start implementing it in our PartOne class.

class PartOne(
    private val sanitizer: Sanitizer
) {
    fun getResult(): Int {
        val data = sanitizer.getItems()
        val totalCalories = data?.map { it.sum() }    // 1
        val mostCalories = totalCalories?.maxOrNull() // 2

        return mostCalories ?: -1                     // 3
    }
}

What our code does is, it creates a new list based on the input in step 1. This new list will contain the summed up values of the calories for each elve. This data structure looks like this

[
  5000,
  4000,
  11000,
  24000,
  10000
]

Next, in step 2 we get the biggest number from the list, which will be 24000. And in step 3 we return that value, or -1 if the input data was null.

Test case

Because we know that we have a list of calories for each elve, we know that we can sum each list to get the total amount of calories for that elve. Once we have the combined calories for each elve we can return the biggest number of combined calories. As you can see in our design diagram, elve four carries the most calories with a combined total of 24000.

So we can write a test case that validates our test input to the outcome of 24000. Right now we can update the PartOneTest class with the following contents.

class PartOneTest {
    @Test
    fun testGetResult() {
        // Arrange
        val resource = {}::class.java.getResource("/input.txt")
        val sanitizer = Sanitizer(resource)
        val sut = PartOne(sanitizer)
        val expectedCalories = 24000

        // Act
        val result = sut.getResult()

        // Assert
        assertEquals(expectedCalories, result)
    }
}