Mazes

Mix.install([
  {:jason, "~> 1.4"},
  {:kino, "~> 0.8.0", override: true},
  {:youtube, github: "brooklinjazz/youtube"},
  {:hidden_cell, github: "brooklinjazz/hidden_cell"}
])

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Setup

Ensure you type the ea keyboard shortcut to evaluate all Elixir cells before starting. Alternatively you can evaluate the Elixir cells as you read.

Overview

In this exercise, you’re going to navigate a maze game.

Each maze is a deeply nested map.

If you navigate successfully, your answer will return "Exit!"

The Atom Maze

We’ve created a map that represents the following maze. Each cardinal direction (north, south, west, east) necessary to navigate the maze is stored as a key in the map.

Use map.key notation to access the "Exit!" string.

Example solution

maze = %{
  south: %{
    west: %{
      south: %{
        east: %{
          south: %{
            east: %{
              south: "Exit!"
            }
          }
        }
      }
    }
  }
}

maze.south.west.south.east.south.east.south

maze = %{
  south: %{
    west: %{
      south: %{
        east: %{
          south: %{
            east: %{
              south: "Exit!"
            }
          }
        }
      }
    }
  }
}

The String Maze

Use use map[key] notation to access the maze and retrieve the "Exit!" string.

Example solution

maze = %{
  "south" => %{
    "east" => %{
      "south" => %{
        "west" => %{
          "south" => %{
            "west" => %{
              "south" => %{
                "east" => %{
                  "south" => "Exit!"
                }
              }
            }
          }
        }
      }
    }
  }
}

maze["south"]["east"]["south"]["west"]["south"]["west"]["south"]["east"]["south"]

maze = %{
  "south" => %{
    "east" => %{
      "south" => %{
        "west" => %{
          "south" => %{
            "west" => %{
              "south" => %{
                "east" => %{
                  "south" => "Exit!"
                }
              }
            }
          }
        }
      }
    }
  }
}

Bonus: Treasure Map

You have been given a treasure map (pun intended). That will lead you to "gold".

Use map[key] and/or map.key notation to retrieve the "gold" value in the treasure_map.

Example solution

treasure_map = %{
  "south ten paces" => %{
    10 => %{
      :"east three paces" => %{
        [1, 2, 3] => %{
          {"turn", "right"} => %{
            :dig => "gold"
          }
        }
      }
    }
  }
}

treasure_map["south ten paces"][10][:"east three paces"][[1, 2, 3]][{"turn", "right"}][:dig]

treasure_map = %{
  "south ten paces" => %{
    10 => %{
      :"east three paces" => %{
        [1, 2, 3] => %{
          {"turn", "right"} => %{
            :dig => "gold"
          }
        }
      }
    }
  }
}

(Extra Bonus) Update the Treasure Map

Use map update syntax to create a update the original treasure_map such that the "gold" is now "taken".

Example solution

treasure_map = %{
  "south ten paces" => %{
    10 => %{
      :"east three paces" => %{
        [1, 2, 3] => %{
          {"turn", "right"} => %{
            :dig => "gold"
          }
        }
      }
    }
  }
}

We can update the treasure map using map update syntax %{old_map | updated_key}.

%{
  treasure_map
  | "south ten paces" => %{
      10 => %{
        :"east three paces" => %{
          [1, 2, 3] => %{
            {"turn", "right"} => %{:dig => "taken"}
          }
        }
      }
    }
}

You might also have found the Kernel.put_in function for updating a deeply nested map.

put_in(
  treasure_map,
  ["south ten paces", 10, :"east three paces", [1, 2, 3], {"turn", "right"}, :dig],
  "taken"
)

Enter your solution below.

treasure_map = %{
  "south ten paces" => %{
    10 => %{
      :"east three paces" => %{
        [1, 2, 3] => %{
          {"turn", "right"} => %{
            :dig => "gold"
          }
        }
      }
    }
  }
}

Bonus: Pattern Matching

Use pattern matching to bind the "Exit!" string to an exit variable.

maze = %{
  "south" => %{
    "east" => %{
      "south" => %{
        "west" => %{
          "south" => %{
            "west" => %{
              "south" => %{
                "east" => %{
                  "south" => "Exit!"
                }
              }
            }
          }
        }
      }
    }
  }
}

BONUS: Create Your Own Maze

Generate a maze using the Online Maze Generator. It should be at least a 5 * 5 in width and height.

• Create a deeply nested map to represent your custom_maze. It should have an "Exit!" value at the end.
• Have a partner navigate your maze using either map[key] notation or map.key notation to retrieve the "Exit!" value.

Enter your solution below.

Mark As Completed

file_name = Path.basename(Regex.replace(~r/#.+/, __ENV__.file, ""), ".livemd")

save_name =
  case Path.basename(__DIR__) do
    "reading" -> "mazes_reading"
    "exercises" -> "mazes_exercise"
  end

progress_path = __DIR__ <> "/../progress.json"
existing_progress = File.read!(progress_path) |> Jason.decode!()

default = Map.get(existing_progress, save_name, false)

form =
  Kino.Control.form(
    [
      completed: input = Kino.Input.checkbox("Mark As Completed", default: default)
    ],
    report_changes: true
  )

Task.async(fn ->
  for %{data: %{completed: completed}} <- Kino.Control.stream(form) do
    File.write!(
      progress_path,
      Jason.encode!(Map.put(existing_progress, save_name, completed), pretty: true)
    )
  end
end)

form

Commit Your Progress

Run the following in your command line from the curriculum folder to track and save your progress in a Git commit. Ensure that you do not already have undesired or unrelated changes by running git status or by checking the source control tab in Visual Studio Code.

$ git checkout -b mazes-exercise
$ git add .
$ git commit -m "finish mazes exercise"
$ git push origin mazes-exercise

Create a pull request from your mazes-exercise branch to your solutions branch. Please do not create a pull request to the DockYard Academy repository as this will spam our PR tracker.

DockYard Academy Students Only:

Notify your teacher by including @BrooklinJazz in your PR description to get feedback. You (or your teacher) may merge your PR into your solutions branch after review.

If you are interested in joining the next academy cohort, sign up here to receive more news when it is available.

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