Question

The Elves begin to set up camp on the beach. To decide whose tent gets to be closest to the snack storage, a giant Rock Paper Scissors tournament is already in progress.

God the question’s description is always pure gold…now let’s jump right in.

We are given a string, our “strategy guide” that represents a rock, paper, scissors turn decision. The string is divided into two columns, the first represents the first player’s decision and the second ours. For example:

 ``````1 2 3 `````` ``````A Y B X C Z ``````

We are also told the following: For player 1 - A = Rock, B = Paper, C = Scissors For player 2 - X = Rock, Y = Paper, Z = Scissors We are also given a score table for the outcome and the decision we made, for example, a win is 6 points and choosing paper is 2 points, etc…

Like previous questions, we’ll start by parsing our input

## Parsing#

We can go (see what I did there?) with several options to represent our game but in my opinion, an array of tuples is the simplest option

 `````` 1 2 3 4 5 6 7 8 9 10 11 `````` ``````func parse(raw string) [][]string { chunks := strings.Split(string(raw), "\n") pairs := make([][]string, len(chunks)) for i := range pairs { pairs[i] = strings.Split(chunks[i], " ") } return pairs } // example output // [ [A, Y], [B, X], [C, Z] ] ``````

The make function allocates a piece of memory in a certain, specified size for our array

## Part 1#

We are asked to provide our total score if we play exactly as instructed in the strategy guide. Let’s think about this for a bit, there are several ways we can solve this, we can use a bunch of `if` statements or some fancy pattern matching, since go does not have pattern matching and I don’t want to write a ton of `if` statements we will go with a hybrid approach. We will create 3 different mappings:

1. Represents the points we get for our choice e.g rock, paper, or scissors
2. Winning state, meaning If we choose X what does the other player need to choose for us to Win
3. Tie state, essentially the same as .2
 `````` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 `````` ``````scores := map[string]int{ "X": 1, "Y": 2, "Z": 3, } // If I choose X(Rock) I need him to choose C(scissors) in order to win win := map[string]string{ "X": "C", "Y": "A", "Z": "B", } tie := map[string]string{ "X": "A", "Y": "B", "Z": "C", } ``````

We don’t take into account the losing state since its essentially a no-op (0 points)

Building on top of these maps and our parsing logic, we can now solve the first part with the following code

 `````` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 `````` ``````func part1(raw []byte) int { pairs := parse(string(raw)) // X Rock, Y Paper, Z Scissors scores := map[string]int{ "X": 1, "Y": 2, "Z": 3, } win := map[string]string{ "X": "C", "Y": "A", "Z": "B", } tie := map[string]string{ "X": "A", "Y": "B", "Z": "C", } score := 0 for _, pair := range pairs { his := pair my := pair score += scores[my] if win[my] == his { score += WINNING_POINTS } if tie[my] == his { score += TIE_POINTS } } return score } // output for part 1 based on the example is // 15 -> (8 + 1 + 6) ``````

At each loop iteration we first add the points based on our choice `score += scores[my]` then we check if `his` move is what we need based on our player choice, to win or get a tie, and if it is we add the necessary points to our total score.

## Part 2#

In part two the sneaky elves switch things up a bit. Instead of our column representing our moves, it represents the turn outcome where X = lose, Y = tie, and Z = win and we need to choose our choice accordingly. For example, let’s look at the first turn `A Y`, the new meaning of this pair is “player one chose Rock, and the game ended in a tie” building on this information we can create new mappings, the new mappings will be between player 1 choice and the choice player 2 need to make to get to a certain state e.g winning, losing, tie, etc… Since it’s pretty similar to part 1, we will jump right ahead and look at part 2 as a whole

 `````` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 `````` ``````func part2(raw []byte) int { var pairs = parse(string(raw)) // X Lose, Y Tie, Z Win scores := map[string]int{ "X": 1, "Y": 2, "Z": 3, } win := map[string]string{ "C": "X", "A": "Y", "B": "Z", } tie := map[string]string{ "A": "X", "B": "Y", "C": "Z", } lose := map[string]string{ "A": "Z", "B": "X", "C": "Y", } score := 0 for _, pair := range pairs { hisMove := pair myMove := pair // we lose if myMove == "X" { score += scores[lose[hisMove]] } // we end in a tie if myMove == "Y" { score += TIE_POINTS score += scores[tie[hisMove]] } // we win if myMove == "Z" { score += WINNING_POINTS score += scores[win[hisMove]] } } return score } ``````

For each desired state we check what move we need to do based on player 2 choice and pass it down to the `scores` map.

That’s it we are all done with paper, rock, scissors and I must admit that I didn’t think it can be so confusing 🤣

You can find the complete code here Thanks for reading!

This post is number 3 of a 13 posts series > Learning Go.