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.

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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:

enter image description here

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:

low-resolution image of a capital letter O

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

the contour of the capital letter O consists of two curves, one for the outer boundary and one for the inner boundary

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

enter image description here

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.


  • 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.


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