# August 2015 Community Challenge

The top-voted answer is Racetrack: "In the game of Racetrack, cars race around a track bounded by two concentric closed loops drawn on a square grid. Implement a program that plays this game."

It's time to choose a for August 2015.

• Post your challenge as an answer to this question. Feel free to resubmit non-winning ideas from previous months.
• Vote for those answers which interest you.
• At the end-of-day on Friday, July 31st, the top-voted post will become the next challenge.

Once the challenge topic is decided, post your solution as a question on the main site and tag it with . The challenge runs throughout August (but nothing stops you from posting an entry later on).

In the game of Racetrack, cars race around a track bounded by two concentric closed loops drawn on a square grid:

Each player has a car at an integer position $(x, y)$ on the grid with a velocity vector $(v_x, v_y)$ that starts at $(0, 0)$. Players take turns to move their cars. A move consists of:

1. updating the velocity vector by adding $-1$, $0$, or $+1$ to each component;

2. moving the car to $(x + v_x, y + v_y)$.

So in the game shown above, the green car's velocity vector went $(1, 0)$ → $(1, 1)$ → $(1, 2)$ → $(0, 3)$ → $(0, 4)$ → $(1, 4)$ → $(1, 4)$ → $(0, 5)$ → $(-1, 5)$.

A car that leaves the track or lands on a position occupied by another car crashes. You'll see that the green car is now doomed: it can't brake quickly enough to avoid running off the top of the track. (There are variations on what happens next: in some versions a crashed car loses the game; in others it can reset its velocity to $(0, 0)$ and continue.)

Implement a program that plays this game.

In image processing, a contour is a closed curve forming the boundary of a region of the image (or a union of closed curves, if the region has holes). For example, given this image:

The contour of the black region is the pair of orange curves shown here:

Implement an algorithm that finds the contour of a region in an image.

You may assume, if you wish, that the image is represented as a two-dimensional array of Booleans (indexed by $x$ and $y$, say), with array entries containing true for the region of interest.

Possible choices of algorithm include:

## Implement Jeopardy

I'd love to see implementations on this classic.

For those who don't know this is the game flow:

• A board is created with several questions.
• Each column is a different category.
• The rows increase question value & difficulty.
• User selects a question & category. Correct answers increase their score by the value of the question, incorrect answers decrease their score just the same, negative scores are possible.

• Questions don't have to be answered, but should feature either a time limit or a 'skip' function.
• if multiple players are enabled(optional):

• the player who correctly answered the last question is the one who chooses the next question.

• If multiple players want to answer, answer priority is given to the one who wanted to answer first and then it goes to the next and so on.

• Play until the board is out of questions.

Pros:

• Well known.
• Can be fully created with just text.

My entry is a FTP server. From there, the quality of the entry is the code & the features included. Can be done in any language, requires no graphical design, and would be a nice challenge.