Puzzles

While having dinner today, I explained how at ilitia we're starting to add to our interviews small puzzles and riddles, not to test if the candidates are very clever but to test how they think and approach a problem, and I thought "If Phobeo posts about development puzzles/riddles, why not posting one or two general ones?".

So here's the first one, the first I knew when I was learning C (development languages are like girlfriends, you never forget the first one ;)

You have 9 dots:

You have to connect all the nine dots, with 4 consecutive lines (if you're drawing in a paper, you can't lift the pen/pencil between drawing the lines).

Example:

This is correct (3 more lines remaining)

This is incorrect (no "curved lines" allowed ;)

I'll post a comment with the solution in a few days, and if you like it, I'll continue posting more from time to time :)

Update: Here's the solution to this first puzzle.