# Advent of Code 2022, Day 2 - Part One

## Preface

Now that we have the following data structure from our previous post, we can start by implementing the business logic to calculate the outcome of each match. Before we can do that, we need to setup two conversion tables. One for converting each strategy and another one to convert each match outcome to points.

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[
{ "A", "Y" }, // Match 1
{ "B", "X" }, // Match 2
{ "C", "Z" } // Match 3
]

### Conversion table for strategies

A for Rock, B for Paper, and C for Scissors […] X for Rock, Y for Paper, and Z for Scissors

Rock | Paper | Scissors |
---|---|---|

A | B | C |

X | Y | Z |

### Conversion table for the match outcome

score for the outcome of the round […] 0 if you lost, 3 if the round was a draw, and 6 if you won

0 points | 3 points | 6 points |
---|---|---|

Rock - Paper | Rock - Rock | Rock - Scissors |

Paper - Scissors | Paper - Paper | Paper - Rock |

Scissors - Rock | Scissors - Scissors | Scissors - Paper |

## Design

Now we know how our data is structured and we gave it a meaning. We can start to think about our business logic. The steps we need to take is that we need to get the points for each match and combine them with the points for each strategy we played.

the score for the shape you selected […] 1 for Rock, 2 for Paper, and 3 for Scissors

So for the sample input we get the following diagram.

```
flowchart LR
subgraph matchone["Match 1"]
direction LR
subgraph strategyone["Strategy"]
direction TB
ao["opponent: <b>Rock</b>"]
ay["you: <b>Paper</b>\n<i>2 strategy points</i>"]
ao ~~~ ay
end
outone["6 points"]
strategyone -- "Play match" --> outone
totalone["Total <b>8 point</b>"]
outone -- "Add <b>2</b> strategy point" --> totalone
end
subgraph matchtwo["Match 2"]
direction LR
subgraph strategytwo["Strategy"]
direction TB
bo["opponent: <b>Paper</b>"]
by["you: <b>Rock</b>\n<i>1 strategy points</i>"]
bo ~~~ by
end
outtwo["0 points"]
strategytwo -- "Play match" --> outtwo
totaltwo["Total <b>1 points</b>"]
outtwo -- "Add <b>1</b> strategy points" --> totaltwo
end
subgraph matchthree["Match 3"]
direction LR
subgraph strategythree["Strategy"]
direction TB
co["opponent: <b>Scissors</b>"]
cy["you: <b>Scissors</b>\n<i>3 strategy points</i>"]
co ~~~ cy
end
outthree["3 points"]
strategythree -- "Play match" --> outthree
totalthree["Total <b>6 points</b>"]
outthree -- "Add <b>3</b> strategy points" --> totalthree
end
sum["Sum()"]
total["Total: <b>15 points</b>"]
matchone --> sum
matchtwo --> sum
matchthree --> sum
sum --> total
```

Once all the matches have been played, and the points calculated we can add all outcomes togheter for our end result.

## Implementation

### Business logic

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

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class PartOne(
private val sanitizer: Sanitizer
) {
fun getResult(): Int {
val data = sanitizer.getItems()
val points = data?.map {
val strategyPoints = when(it.second) { // 1
"X" -> 1 // Rock
"Y" -> 2 // Paper
else -> 3 // Scissors
}
val roundOutcome = when(it) { // 2
// Lost
Pair("A", "Z"),
Pair("B", "X"),
Pair("C", "Y") -> 0
// Draw
Pair("A", "X"),
Pair("B", "Y"),
Pair("C", "Z") -> 3
// Won
else -> 6
}
strategyPoints + roundOutcome
}
val totalRoundsOutcome = points?.sum()
return totalRoundsOutcome ?: -1;
}
}

What our code does, is, it turns our matches list into a list of round outcomes. At *step 1* the strategy points are calculated based on the information we’ve gotten from the assignment. We only check for our own moves, because we don’t get points for the move the opponent made.

Once we’ve gotten the score from our strategy, we calculate the points based on the round outcome. At *step 2* we only check for winnings and a draw. This can be cleaned up by splitting it into a seperate method or normalizing the data into `Rock`

, `Paper`

and `Scissors`

instead of the current `A`

, `B`

, `X`

etc.

So this will give us the following data structure.

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[
8,
1,
6
]

This list is finally summed up and return as the assignment outcome.

### Test case

Because we know that we have a list of all round outcomes, we know that we can sum each item in the list to get the total score. As you can see in our previous diagram, the total score of the sample input will be **15**.

So we can write a test case that validates our test input to the outcome of **15**. Right now we can update the `PartOneTest`

class with the following contents.

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class PartOneTest {
@Test
fun testGetResult() {
// Arrange
val resource = {}::class.java.getResource("/input.txt")
val sanitizer = Sanitizer(resource)
val sut = PartOne(sanitizer)
val expectedNumberOfPoints = 15
// Act
val result = sut.getResult()
// Assert
assertEquals(expectedNumberOfPoints, result)
}
}