Four implementations of Conway's Game of Life (https://coderetreat.com/gol.html)

These are the four programs I co-wrote with 4 people (sorry, I don't remember everyone's names)
for the December 3, 2011 SF Code Retreat (https://coderetreat.com/)
Each attempt was limited to 45 minutes.

1) First attempt, no tests, grid-based, starting to figure out how to count neighbors.
2) Test-driven. Got setup and neighbor counting working.
3) Different approach - using a set of coordinates of active cells instead of a grid.
4) Pulled together everything we had learned so far. Fewer tests this time, with focus on getting a working solution. Success!