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 22: Langton's Ant

2017-12-22

Source: Sporifica Virus

Part 1: Implement a cellular automaton on an infinite grid of . and # pixels such that:

  1. Start at (0, 0), facing Up
  2. Repeat:
  • If the cursor is on . swap it to # and turn Left
  • If the cursor is on # swap it to . and turn Right
  • Either way, after turning, move forward once

After 10,000 iterations, how many pixels were turned from . to #?

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AoC 2017 Day 21: Fractal Expander

2017-12-21

Source: Fractal Art

Part 1: Start with an input image made of . and # pixels. For n iterations, break the image into blocks:

  • If the current size is even, break the image into 2x2 chunks and replace each with a 3x3 chunk
  • If the current size is odd, break the image into 3x3 chunks and replace each with a 4x4 chunk

The replacement rules will be specified in the following format (example is a 3x3 -> 4x4 rule):

.#./..#/### => #..#/..../..../#..#

In that example, replace this:

.#.
..#
###

With this:

#..#
....
....
#..#

Any rotation or reflection of a chunk can be used to match the input of a replacement rule.

After n = 18 iterations, how many # pixels are there?

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AoC 2017 Day 19: Networkout

2017-12-19

Source: A Series of Tubes

Part 1: Take a network diagram of the following form:

|          
|  +--+    
A  |  C

F—|–|-E—+ | | | D +B-+ +–+


> Starting at the single node at the top and following the lines, what order would the nodes be visited in?





First, load the entire network:

```python
data = {}
points = {}
entry = None

def is_point(c):
    return re.match('[A-Z]', c)

for y, line in enumerate(lib.input()):
    for x, c in enumerate(line):
        if c.strip():
            data[x, y] = c

        if is_point(c):
            points[c] = (x, y)

        if y == 0 and c == '|':
            entry = (x, y)

Then, calculate the path:

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AoC 2017 Day 18: Duetvm

2017-12-18

Source: Duet

Part 1: Create a virtual machine with the following instruction set:

  • snd X plays a sound with a frequency equal to the value of X
  • set X Y sets register X to Y
  • add X Y set register X to X + Y
  • mul X Y sets register X to X * Y
  • mod X Y sets register X to X mod Y
  • rcv X recovers the frequency of the last sound played, if X is not zero
  • jgz X Y jumps with an offset of the value of Y, iff X is greater than zero

In most cases, X and Y can be either an integer value or a register.

What is the value recovered by rcv the first time X is non-zero?

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SSH Config ProxyCommand Tricks

2017-12-18

Working in security/operations in the tech industry, I use SSH a lot. To various different machines (some with hostnames, some without), using various different users and keys, and often (as was the case in my previous post) via a bastion host. Over the years, I’ve collected a number of SSH tricks that make my life easier.

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AoC 2017 Day 17: Spinlock

2017-12-17

Source: Spinlock1

Part 1: Start with a circular buffer containing [0] and current_position = 0. For n from 1 up to 2017:

  1. Step forward steps (puzzle input)
  2. Input the next value for n, set current_position to n, increment n
  3. Repeat

What is the value after 2017?

It’s a bit weird to describe, but the given example helps (assume steps = 3):

(0)
0 (1)
0 (2) 1
0  2 (3) 1
0  2 (4) 3  1
0 (5) 2  4  3  1
0  5  2  4  3 (6) 1
0  5 (7) 2  4  3  6  1
0  5  7  2  4  3 (8) 6  1
0 (9) 5  7  2  4  3  8  6  1

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