Programming

The earliest memory I have of ‘programming’ is in the early/mid 90s when my father brought home a computer from work. We could play games on it … so of course I took the spreadsheet program he used (LOTUS 123, did I date myself with that?) and tried to modify it to print out a helpful message for him. It … halfway worked? At least I could undo it so he could get back to work…

After that, I picked up programming for real in QBASIC (I still have a few of those programs lying around), got my own (junky) Linux desktop from my cousin, tried to learn VBasic (without a Windows machine), and eventually made it to high school… In college, I studied computer science and mathematics, mostly programming in Java/.NET, although with a bit of everything in the mix. A few of my oldest programming posts on this blog are from that time.

After that, on to grad school! Originally, I was going to study computational linguistics, but that fell through. Then programming languages (the school’s specialty). And finally I ended up studying censorship and computer security… before taking a hard turn into the private sector to follow my PhD advisor.

Since then, I’ve worked in the computer security space at a couple of different companies. Some don’t exist any more, some you’ve probably heard of. I still program for fun too, and not just in security.

But really, I still have a habit of doing a little bit of everything. Whatever seems interesting at the time!

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AoC 2017 Day 7: Tree

2017-12-07

Source: Recursive Circus

Part 1: A tree is defined as such:

  • node (weight) -> child1, child2, ...
  • node (weight)

Where a node always has a weight, but may or may not have child nodes.

What is the name of the root node of the tree (the node without a parent)?

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AoC 2017 Day 6: Tightrope

2017-12-06

Source: Memory Reallocation

Part 1: Start with n stacks of different sizes. Take the largest block and distribute its items starting with n+1 and looping around. How many iterations of this does it take before you see a state you’ve seen before?

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AoC 2017 Day 3: Spiraly

2017-12-03

Source: Spiral Memory

Part 1: Create a grid in a spiral pattern like so:

17 16 15 14 13 18 5 4 3 12 19 6 1 2 11 20 7 8 9 10 21 22 23—> …


> Given a specific index, what is the [[wiki:Manhattan Distance]]() from that point to the origin (`1`)?





This same sort of structure comes up from time to time in [Project Euler](/programming/sources/project-euler/) as well. I'm going to guess we'll see this again. Seems like a fine contender for a [library function](https://blog.jverkamp.com/2017/12/01/aoc-2017-library-functions/).

Specifically, we'll create a `SpiralGrid` class that can be used to automatically generate as large of a grid as we want lazily (it won't generate more of the grid until we need it).

```python
class SpiralGrid():
    '''
    Generate a spiral grid that looks like this:
    17  16  15  14  13
    18   5   4   3  12
    19   6   1   2  11
    20   7   8   9  10
    21  22  23---> ...

    The point (0, 0) is 1. x runs left to right, y from top to bottom. So the
    point 12 is at (2, -1).
    '''

    def __init__(self):
        self._indexes = {}
        self._points = {}

        def make_spiral():
            index = 1
            (x, y) = (0, 0)

            yield index, (x, y)

            # Build the layers outwards
            for layer in itertools.count(1):
                # Each layer starts by going right and down one (we'll go back up before yielding)
                x += 1
                y += 1

                # Go through the four sides, up then left then down then right
                # Repeat 2*layer times per side
                for xd, yd in [(0, -1), (-1, 0), (0, 1), (1, 0)]:
                    for step in range(2 * layer):
                        index += 1
                        x += xd
                        y += yd
                        yield index, (x, y)

        self._generator = make_spiral()

    def __getitem__(self, key):
        '''
        Given an index or point return the other.

        If we're given an integer, it's an index, return the point.
        If we're given a tuple, it's a point, return the index.

        Either way, generate as much data as we need and don't have.
        '''

        if isinstance(key, int):
            field = self._indexes
        elif isinstance(key, str):
            key = int(key)
            field = self._indexes
        elif isinstance(key, tuple) and len(key) == 2:
            field = self._points
        else:
            raise ValueError

        while key not in field:
            index, point = next(self._generator)
            self._indexes[index] = point
            self._points[point] = index

        return field[key]

The neat part here is using a generator to generate the coordinates of points. That way, we can run the generator until we find the point we’re looking for and cache any results for later.

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AoC 2017: Library Functions

2017-12-01

As mentioned in the main post, I’m structuring my solutions a bit differently this year. Rather than repeating the same relatively lengthy header in each function, we’re going to have a few shared files that can be imported or used for every problem.

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Clock drift in Docker containers

2017-11-15

I was working on a docker container which uses the aws cli to mess around with some autoscaling groups when I got a somewhat strange error:

A client error (SignatureDoesNotMatch) occurred when calling the DescribeAutoScalingGroups operation: Signature not yet current: 20171115T012426Z is still later than 20171115T012420Z (20171115T011920Z + 5 min.)

Hmm.

Are the clocks off?

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