AoC 2022, Day one - Part Two

Preface

Now that we have the following data structure from our previous post, we started implementing the business logic to retrieve the three highest combined number of calories and add them together.

[
  [ 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 second part of the assignment is to retrieve the three highest amounts of combined calories a single elve is carrying, and them adding those three combined calories together. So we need to sum up all the calories in each list from our data structure and get the three biggest numbers. Once we have those three numbers, we need to add them together for our final result.

Implementation

Business logic

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

class PartTwo(
    private val sanitizer: Sanitizer
) {
    fun getResult(): Int {
        val data = sanitizer.getItems()
        val totalCalories = data?.map { it.sum() }              // 1
        val sortedCalories = totalCalories?.sortedDescending()  // 2
        val topThreeMostCalories = sortedCalories?.subList(     // 3
            fromIndex = 0,
            toIndex = 3 // toIndex is three instead of two because it's exclusive
        )
        val mostCalories = topThreeMostCalories?.sum()          // 4

        return mostCalories ?: -1
    }
}

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 sort the new list in ascending order. Thus the highest number is placed in the front of the list, and the smallest number at the end of the list. We then retrieve the first 3 items from that list in step 3, as those are the three biggest numbers in the list.

Then finally we sum up the three numbers in that list, and return that value.

Test case

Because we know that the three biggest numbers from the elves are 11000, 24000 and 10000, we can add them up to get a total of 45000 and use that as our expected outcome in the test case.

So we can write a test case that validates our test input to the outcome of 45000. Right now we can update the PartTwoTest class with the following contents.

class PartTwoTest {
    @Test
    fun testGetResult() {
        // Arrange
        val resource = {}::class.java.getResource("/input.txt")
        val sanitizer = Sanitizer(resource)
        val sut = PartTwo(sanitizer)
        val expectedCalories = 45000

        // Act
        val result = sut.getResult()

        // Assert
        assertEquals(expectedCalories, result)
    }
}