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. That’s about where I am today!

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

Advent of Code 2016

2018-01-03

As I did last year, I’m going to solve the Advent of Code problems again this year.

Or that was the plan. It turns out that instead I put down my blog for almost a year and a half and never quite got around to doing these problems. So I’m actually backdating these posts from the early days of 2018 to where they would have been had I solved them on time. They’re still interesting problems, so give them a read.

AoC 2017 Day 25: Turing

2017-12-25

Source: The Halting Problem

Part 1: Implement a Turing machine defined as such:

Begin in state A. Perform a diagnostic checksum after 6 steps.

In state A: If the current value is 0: - Write the value 1. - Move one slot to the right. - Continue with state B. If the current value is 1: - Write the value 0. - Move one slot to the left. - Continue with state B.

…

AoC 2017 Day 24: Maker Of Bridges

2017-12-24

Source: Electromagnetic Moat

Part 1: Given a series of reversible components of the form 3/4 (can connect a 3 on one end to a 4 on the other), form a bridge of components. The bridge’s strength is equal to the sum of component values. So 0/3, 3/7, and 7/4 has a strength of 0+3 + 3+7 + 7+4 = 24.

What is the strongest possible bridge?

AoC 2017 Day 23: Duetvmc

2017-12-23

Source: Coprocessor Conflagration

Part 1: Create a variation of the previous DuetVM with only the following four instructions:

set X Y sets register X to Y
sub X Y set register X to X - Y
mul X Y sets register X to X * Y
jnz X Y jumps with an offset of the value of Y, iff X is not equal to zero

If you run the given program, how many times is mul invoked?

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:

Start at (0, 0), facing Up
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 #?

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?

AoC 2017 Day 20: Miniature Universe Simulator

2017-12-20

Source: Particle Swarm

Part 1: Given the initial position, velocity, and acceleration of a large number of particles, which particle will stay the closet to the origin as the simulation runs to infinity?

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-+ +–+

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?

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.