Phone II

Here are two screenshots of the Android 3×3 grid lock we dealt with in the phone post.



Part of the reason I don’t have a real post today and am instead writing filler for the streak is that I wanted to include this 3×3 lock in the programming presentation I’ve been indirectly complaining about in the last few posts, and I couldn’t find any nicely licensed screenshots to illustrate it, so I made these screenshots myself, and then I spent somewhat more than an hour researching copyright law and listening to a talk about it before posting them.

I’m pretty sure screenshots fall under fair use: the usage is noncommercial and educational, the screenshot is a very minuscule portion of the phone and provides no competition whatsoever with people who actually want to use a phone. And Android is open-source (Apache License 2.0, GNU GPL 2.0 for Linux kernel modifications) so actually I probably shouldn’t need to bother with this at all. Oops.

The background is a picture from roloox on dA, which is CC BY-NC 3.0. That’s why. I’m still here wishing more people CC-licensed their stuff.

To whatever degree it’s necessary for me to do this, these screenshots are released under CC BY-SA as usual, although the background would probably require noncommercial usage anyway, and getting these screenshots could easily fail to meet the threshold of originality. (It’s actually not very easy to get these because you need one finger held on the lock and two fingers simultaneously pressing and holding the power button and the volume down button. Also, I gave away my home city. Haha oops. (But this disclaimer actually has nothing to do with supporting claims of originality; it could only tend towards supporting copyrightability under “sweat of the brow” doctrine, which Wikipedia says countries are moving away from. The only thing I did originality-wise was to get the second path to illustrate a knight’s-move and two path-segment-midpoints, one of which was visited once and one of which was visited twice. Obviously not very convincing.))

…ugh, how did I end up writing so many words for a filler post?


MIT Course Number Mnemonics

When I first realized it might be helpful to start trying to remember the correspondence between MIT courses and their numbers, I expected a list of mnemonics for this correspondence would be one of those Things That Should Exist On the Internet. I’m pretty surprised it doesn’t. I mean, MIT has, what, at least 100,000 alumni; as far as I know, nearly everybody who goes there speaks the number correspondence fluently, so they have to learn it; and the science of mnemonics has been with us since the ancient Greeks and people who understand its usefulness can’t be uncommon, especially not in such a prestigious institute of higher education.

What gives?

I’m not sure. Maybe it’s just that nobody has posted their mnemonic set on the Internet out of embarrassment? My mnemonics are pretty bad too, but hey, Cunningham’s Law — if you’re reading, feel free to add better ones in the comments, or to criticize my horribly unenlightened and stereotypical characterizations of your courses, to make this thing better. Or maybe it’s out of concern that nobody else will find it useful? I get that feeling but my streak compels me to ignore it now, as it has for the last dozen posts or so. Or maybe they just didn’t optimize for search engine findability, so I can’t find it? I hope this post fixes that.

Actually, I guess the most likely reason is that maybe most people don’t actually have all the course numbers memorized with perfect recall, only the handful of most common ones they and their friends are in, and it’s perfectly fine to ask for clarification when an unknown number comes up in conversation, so nobody ever feels like they need to bother with mnemonics for every single course. Feels sensible to me.

But anyway, I’m not most people.

The most comprehensive resource of courses and numbers, including their history, appears to have once been at Many, many links point there. Unfortunately, it is dead and I cannot find its new home, if it has one. Fortunately, there is an archived version on; on the other hand, I am not sure whether any updates have occurred since it was archived. A more recent version with course populations from 2005 is this chart linked from the MIT Admissions blog post Numbers are names too.

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tl;dr: anybody want to add me on Line or tell/remind me about other phone chat apps? betaveros as always.

Wow, talk about uninspired post titles.

I got a new phone today. Or, well, it’s second-hand, actually. I try to make electronics last a long time, but I think this was justified given the state of my last phone’s screen:

old phone screen, with a visibly malfunctioning black patch

Besides, I’m going off to college and all. Anyway, the phone is pretty cool. It’s a slick shade of red, it came with a cover and everything, and it has one of those fancy 3×3-grid locks. How secure are those again?

Well, we could just find the answer on StackOverflow, but that’s boring.

*ahem* Here we go, Literate Haskell. Plumbing:

> import Control.Applicative
> import Control.Arrow
> import Control.Monad
> import Control.Monad.Trans
> import Control.Monad.Trans.State
> import Text.Printf

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= within 15 cents of $20,000/7
= NT$88,661, by Google’s current exchange rate

= 739 hours of Taiwan’s hourly minimum wage or 4.43 months of Taiwan’s monthly minimum wage
= 317 hours of Massachusetts’s minimum wage (7.94 weeks or 1.85 months assuming a 40-hour work week)
= 1.2~1.7 weeks of a list of high tech internship salaries as featured on Slate

= 2,955 plates of Sushi Express
= 1,478 cheap boxed lunches (at NT$60 each), which would last one person 1.35 years at 3 per day
= 1,122 Big Macs, price in Taiwan, or 596 Big Macs, average price in U.S. (January 2015)

= 956 copies of Blackbar
= 573 copies of Hadean Lands
= 286 copies of Spacechem
= 181 nanoblock Charizards
= 95 years of reddit gold
= 56 copies of everything by Pentatonix on iTunes (U.S. pricing)
= 28 years of a minimal WebFaction server
= 24 years of a minimal Linode server
= 12 unicorns
= 4.5-ish copies of the entire set of Pokémon games (I just Googled this; I hope it’s accurate)
= 1.8 MacBook Pros (256GB) (educational price with 3-year warranty)
= 1.08 standard Individual Licenses for MATLAB ($2,650. What. I can’t even.)

= 3.6 dead children, original figure quoted on
= 0.86 dead children, 2015 estimate from GiveWell’s assessment of Against Malaria Foundation

= 88% of an APMO gold medal
= 44% of an IMO gold medal

= 0.0000016% of Taiwan’s national debt = 39% of debt per person
= 0.000000016% of U.S. national debt = 5% of debt per person

This is going to be dwarfed by the airplane tickets and meals anyway, so I don’t know what I’m doing.

Well, no, I do know what I’m doing: making filler posts for the streak.

Also, I’m sorry for the arbitrariness of the sigfigs.

Cognitive Asymptotics

Short blog content for daily posting streak. Standard disclaimers apply. Not much to see here.

At some point in the past, because I was a bored teenager, I memorized this.

So now, in theory, I can tell you the capital of each state of the U.S. This is already a lame trick, but as I realized yesterday, it’s made even lamer by the fact that the data structure I chose only supports O(n) lookup.

This is really slow! Moral of the story: Asymptotics matter.

P.S. Okay, to be pedantic, since the number of states in the song is pretty much fixed at 50, any lookup method is O(1), and I made that argument once before myself. But you know the intuitive sense I’m trying to get at.

The Beginning of the End

One sentence from my new guidance counselor was all it took.

“Oh, you’ll need a 2350 on the SAT and a 4.3 GPA to get into Caltech.”

I even instinctively knew that those were grossly inflated numbers, a guess that was borne out by investigation — a quick check at Caltech’s website verifies that 2350 would be in the top quartile.

(Just in case you’re wondering, that particular college was chosen under duress for a research project, and I consciously stayed away from colleges that I knew students of in order to get a more balanced view of everything. Don’t read too much into it.)

Doesn’t matter. I still immediately had to prove myself to a person who I barely knew yet.

I thought I was above this.

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MUMS Puzzle Hunt 2013


So, I somehow managed to get 25 points all by myself in MUMS Puzzle Hunt 2013. Well, I pestered chaotic_iak a little with 3.3 Diagnosus (.html with animated .gif) but we still didn’t recognize all the Pokémon until hint 3, at which point Google sufficed for me.

This is nowhere near the top, but compared to the usual results of whatever AoPS team I form, it’s amazing. By far the best result of AoPS was on CiSRA in 2010 (46th with 58 points), before I discovered puzzle hunts in AoPS; unfortunately due to people getting older and the influx of younger and younger people to the fora, there are less possible teammates each year and they have less time, so here I am by myself. (Also I could have accepted an invitation from a guy in the some-form-of-Elephant team, but I figure if you can win two MUMS hunts in a row you don’t need any more people.)

All in all: Yay!

If you are a logic puzzler, you’ll probably be most interested in 2.2 Informatix (PDF), 3.4 Sokobus (.html with Unity embed, interactive), and 5.2 Psychoanalytix (PDF). Psychoanalytix is the most traditional logic puzzle on a grid, although you have to guess the rules (which are, however, provided in hint 2); Informatix is (I think) closest to completely logical. But you still have to figure out how to extract the answer yourself.

I should probably also mention 1.3 Cryptograf (PDF). I think this is the first puzzlehunt puzzle I’ve seen where I have an advantage in cultural knowledge! (I don’t count things like finite fields or Morse code as culture. Also, I’m guessing that I know more about Pokémon than the average person but less than the average puzzlehunter.)