Programmer tries to explain binary search to the police
Programmer tries to explain binary search to the police
410 comments
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Yeah, pigs don't like to be corrected. Or made to look like they don't know what they're doing.
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And they absolutely hate ever doing anything about bicycle theft in particular.
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It probably depends a lot on where you live. My wife's bike got stolen and she was woken up by police coming to check on it (one of the maintenance guys at our apartment noticed a man at 7-Eleven riding it and recognized it; came back running to check if it's indeed missing and called the police). We fully expected the police would do nothing about it (it was the cheapest Walmart bike), but an hour later they called that they found the bike and have the culprit in custody. It did help that the bike was a girly mint green with a wicker basket, so they instantly recognized it when they saw it.
Then again, in San Francisco, when my wife got her car window smashed and wallet stolen (she was late for class and dropped her wallet under the car seat, didn't stop to take it; but it wasn't the wallet that caught the thieves' attention, it was the breast pump bag that looked like a laptop bag; they threw it on the floor when they saw what it was), we never heard anything back from the police.
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And they absolutely hate ever doing anything
about bicycle theft in particular.FTFY
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Fun fact. Cops on average have lower IQ and often fail literacy tests. Furthermore it appears that critical thinking is discouraged in the job, with candidates being selected who lack critical thinking abilities over those that have them.
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This argument did not go well
You can't convince people to do their job with logic when they just don't want to do their job. After minorities, the thing cops hate most is doing their job.
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WRONG! After minorities, it's poor people. Then doing their job. :P
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Come on, don't disparage our hard-working Boys in blue. Without police who's going to come to your house to take notes about the crime that you have sufficient evidence to prove, and even have a likely suspect for, and then never follow up?
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when they just don’t want to do their job.
It might also be a matter of getting a directive from their management not the care, because there's not enough cops to go around for the 'important' stuff.
They don't want to waste their limited time for simple property theft, which is ironic considering that's what police are supposed to be doing (stopping theft).
The answer would be then to hire more police, but unfortunately that would mean higher taxes for the citizenry, and that seems to be a hard glass ceiling.
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No, the police just don't want to do any work. In my hometown you can't get the police to do shit unless you are a black man who "fits the description" or "smells like weee" then they will gladly try to make your death look as much your fault as possible.
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More police wouldn't cost more money if they stopped buying tanks.
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I thought this had to be hyperbole, so I did the math myself. I'm assuming human history is 200,000 years as google says, and we want to narrow this down to the second the bike disappeared. also that the bike instantly vanished so there's no partially existing bike.
each operation divides the time left in half, so to get from 200k years (6.311×10^12 seconds) to 1 would take ~42.58 divisions, call it 43. even if we take a minute on average to seek and decide whether the bike is there or not it would still be less than an hour of manual sorting
hell, at 60fps it would only take another 6 divisions to narrow it down to a single frame, still under an hour
edit: to use the entire hour we'd need a couple more universes worth of video time to sort through, 36.5 billion years worth to be exact. or a measly 609 million years if we need to find that single frame at 60fps
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I regularly bisect commits in the range of 200k (on the low end) for finding causes of bugs. It takes me minutes. Pretty crazy
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Lemmy learns exponential math.
Mostly joking, thanks for doing the math.
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History is about 10k years, the 200k years is mostly pre-history. People didn't write stuff down until they invented agriculture and needed to track trade between owners, workers, etc
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Just watch at 3X!
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Combine AI image/visual-pattern recognition and quantum computing, and this search could be completed before it was even started.
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We can go deeper!
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A minute to decide if there is a bike in the picture really ?
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As a robot, finding bikes in pictures is really hard, okay
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Takes time to precisely seek to each timestamp, but really I just meant that an hour was reasonable even with a lazy cop doing the search
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They must be really bad at solving CAPTCHA
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Ever heard of a logarithm? If you haven't, you just reinvented it.
Also, your math is wrong: log base 2 of 200,000 is ~18
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You did 200k years. You need to do 200k years as seconds (the 6.311e12 they mentioned). Their math is right.
Not sure why you're acting like they claimed to invent the logarithm, either...
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This didn't go down well.
IT consulting pro-tip: Customers would rather pay for your time and expertise, than be made to feel stupid that they didn't think of something so simple themselves.
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After working in desktop support for a year after college, I realized that people just wanted their problem solved and to not feel frustrated. That realization made my job immensely easier because I pivoted from copying a file in 30 seconds and walking away to talking to them a little bit and letting them feel good after we were done. My ticket closing speed slowed down a little but people felt better and I consistently got positive feedback.
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Dude same here. I usually say stuff along the lines of 'yea it took me forever the first time to figure it out' or 'it's a common issue that a lot of people have, I'll get it sorted in a sec for you no problem'. Make it seem like they're not stupid, regardless of the truth and then fix it, keeps em happy and more willing to cooperate with you as well.
I also talk through what I'm doing and if they show interest I'll teach them so they can fix it in the future, 'ah I've seen this before, took me like a hour to figure it out on my computer, for me it was a chrome update that broke how downloaded files open. Here let me right click the file, and go to open with, we hit Adobe pdf and check the always open with this program button, that should do it let's test it out. OK seems like its good to go. Let me know if you have any more issues'. If they don't show interest then it's no problem.
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Same story here, actually. I cut my teeth on internet telephony (modems) support for an ISP. People would call up furious about not being able to connect. I learned that chatting people up during a long Windows reboot did a lot to humanize their struggle and get them to calm down and loosen up. First few times were organic, then I started looking for pretenses to do this, just to bring the temperature down for the rest of the call.
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Just yesterday, I was helping this manager set up a new system of ticket line (the kind where you get a ticket number and wait for it to be called in a panel). He complained that they didn't have a proper printer just for these tickets, so he made the tickets in excel and printed them. To the right of the number, someone would mark the service, from a list of 6.
"Why not use a single letter prefix and print different piles of passwords? (A01, A02, A03; B01, B02, etc)"
That'll use too much paper. We'll also need more tickets than before
"That will use less paper, you can print 2 tickets using the same space. Also, the amount of tickets always depends on the number of people that show up, but you'll have a better idea of which service is being needed each day"
Mr manager didn't like the idea and moved on to another problem.
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Eh, it's less intuitive than you might think, as someone who already knows how to do it.
I once had to explain this process to a software engineer who was quite senior to me. The guy wasn't any idiot, he was a pretty competent engineer, he just didn't know this trick.
The cops might even already know how to do it, they just don't want to, because they're cops.
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This method will take forever to find the exact moment, said Officer Zeno.
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I love you for that joke.
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I heard that he wanted to get Officer Thomson and his lamp on the case, but the request form was incomplete.
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I'm a little surprised the police didn't already know about that method. Seems like they'd encounter enough CCTV footage that'd it'd be standard training.
I once again overestimate the training levels of the police.
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They probably do know. They just aren't meant for protecting your personal property
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Right.
What they really want to say is "We aren't interested in investigating your personal theft. Things get stolen all the time and we really can't be bothered. You are not important to us."
But they can't say that, so they instead throw out some excuse that puts the onus back on the other person.
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And Detective Conan Doyle O'Brien really did just let his bro fuck around and watch porn and even bring a stripper into the station during footage reviewing hours. Of course, Stuart was quite shocked to hear he was not invited to the stag do later that weekend
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For sure they know, it's just cops are lazy and aren't paid to solve crimes
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I imagine it's utilized in more "serious" investigations and they just can't be arsed for theft.
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In the US most their training involves how to be more aggressive veiled as training to be assertive.
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It’s a somewhat narrow situation. You won’t always have the object of interest in plain view of a camera. What if it’s behind a door? Well now you do have to scrub through all the footage
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This post just shows that the police rarely if ever review any video as this method would've been learned as a result of repeatedly reviewing video.
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Part of my job is to review security footage for reported incidents.
If there is a long-lasting visual cue that the event has or has not happened yet (e.g. a window is either broken or not), then a binary search is very useful.
If the event lasts only a moment and leaves no visual cue (e.g. an assault), then binary search is practically useless.
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If the event lasts only a moment and leaves no visual cue (e.g. an assault), then binary search is practically useless.
But you will see the event happen though.
It's a matter of if you can identify who the perpetrator is or not, but at least that due diligence should be done by police, looking at the person doing the crime and see if they can be identified.
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Let's use the example of a bike theft. We enter into evidence a 4-hour security cam video that shows the thief with the bike.
Scenario A: The camera can directly see the bike rack, and the bike in question is visible at the beginning of the video, and not visible at the end. Somewhere in this 4-hour video, someone walks up to the bike and takes it out of the bike rack. You can use a binary search to find the moment that happens in this video because you can pick a frame and say "Ah, this was before the theft; the bike is still there" or "ah, this was after the theft; the bike is gone."
Scenario B: The camera can't directly see the bike rack, but can see the doorway you have to walk through to get to the bike rack. So somewhere in 4 hours of doorway footage, someone walks through the door, then a short time later walks back through the door with the bike. A binary search won't help here because the door looks the same at the beginning or end of the video. A simple binary search won't work here because the door looks the same before and after.
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I'm just a random guy stumbling across this thread hours after the fact. I want to say that after reading many of these comments. I feel like I'm starting to get a handle on what your position is. You aren't wrong, but you are communicating your idea horribly.
Your position seems to be "Thankfully, many crimes do leave behind lasting visual cues, so you can still do a binary search for those situations if you are clever about what to look for."
What you've actually been communicating is that "If there really was no lasting visual cue, then just find a lasting visual cue anyway, then do a binary search on that and it'll work!" - It's all about how you choose to present, order, and emphasize your comments. Your message is more than just the words you type. I hope this message helps clarify the debate and confusion for you and anyone else who stumbles upon this long chain.
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Police try to understand anything challenge (100% impossible) (gone sexual) (gone violent)
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I once had a friend who was robbed of all kinds of stuff including a PS3, and that the guy was signed into his Netflix changing account profiles the very same day. I told him he can just get a tracking number by calling Playstation and that the active police officer can use it to track them. Thing is, the officer ghosted him for like 8 months despite having everything they needed to immediately find the exact location of the perpetrator actively using the stolen property.
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They don't care really. As has been my experience anyway.
I once had my car window smashed, a mix of gear taken..some was expensive, some was personal to me. I felt violated. Called the police, explained, gave S/Ns to what I could, told them exactly who did it. He didn't give a shit. Actually made me feel like I was wasting his time. I think Seinfeld covered this..
"We'll let you know if we find anything" "Do you ever find anything?" "No"
But oh, my reg is out of date and the plate scanner picked it up? Boom, they really kick it into gear. So that's $130.. i could just go take care of the tags immediately with a friendly warning but now don't even want to. And in the end I end up pretty fucked.
If only they put that effort into other things I just might have gotten my linear power amps back. Props to anyone who knows that product.
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That's how I look for broken mods too. Move half of them into a temp folder, launch the game. If it works, put half of the sorted out ones back. if it doesn't work, remove another half and try again.
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This is all fine and good till it's a conflict between two specific mods. Damn you FO4 on PS4, why you gotta be like that?
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When I want to see a broken mod, I just surf over to Reddit.
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Btw, this is why i have given up on Early Access on Steam; can't disable updates and have to fix your 100 mods then.
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I love Steam, but the fact that you cannot permanently disable auto updates for specific titles is definitely infuriating.
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Yeah, pretty great in my minecraft modding experience
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I was looking for this specific comment lmao
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"Exactly my point. We will not be investing an hour looking at the footage to pinpoint the time of theft, now get out!"
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Show up with a box of donuts.
"Hey, look what I got for us to eat while looking at that tape!"
"Oh, I don't think those donuts will last more than ten minutes here!"
"No problem, I know a way that won't take that long..."
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just tell them there is a black man at the moment of theft, they will get on it lickety split!
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- Binary search: O(log(n))
- Sequential search: O(n)
- Linear search: O(n)
- Police ethnicity database search: O(0)
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No need to search when you already have someone you wanna pin it on.
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Sad meme very relevant
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I'm sure it didn't go well. If it was somehow framed in a sycophantic way where the police were led to believe it was their idea, I'm sure it would have gone better. Wait that might not be too difficult to do.
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You just have to say there was a weird technique the Nazi's liked to use.
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They probably already know all Nazi techniques.
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Na. If it's British police it's just an excuse. All they're there for after all these years of Tory cuts is to give you a reference number so you can make an insurance claim.
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Sounds about right. Cops have low iqs
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more importantly cops don't actually give a shit about solving crime.
In England the police primarily exist to keep noise down in middle class areas. I assume it's even worse in America
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That is their primary purpose here too but it just requires more violence and subjection, Americans are extra noisy.
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It would have taken 5 minutes at most
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My Graphics card/ssd wouldn't be able to handle the skipping of such big files
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Yeah, even if it was from the beginning of dawn. No need to check out tape before the guy parked his bike.
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But thats 5 minutes of killin' time they'll never get back
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On my site's security nvr, it takes five minutes just to convince it that you want to search a particular camera
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Their method actually does make sense, you just have to remember they aren't cops to solve (boring) crimes like petty theft. Why get it done as efficiently as possible when you can milk it for hours of overtime? 12 hours of footage means 6+ hours of overtime even watching it at x2 speed, and it's the kind of thing you can basically have going on in the background. Cops being willfully ignorant for their own benefit makes sense to me
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You know what's even better than milking it for 6hrs of OT? Saying its "to hard" to the victim, going home and then lying about doing 6hrs of OT and getting paid anyway.
Cops lie about OT systemically. Its absolutely rampant. The only consequence they ever get is either a few hrs suspension without pay or fired, and most states are happy to hire them next door immediately so they can do it again.
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“This argument didn’t go down well.”
🤣🤣🤣 LMAO
What an awesome punchline, should have been on its own line for more impact.
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When troubleshooting physical systems, it's called half-splitting
https://www.ecmweb.com/maintenance-repair-operations/article/20889049/the-beauty-of-halfsplitting
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This is fault finding 101 for fire alarm systems.
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God damn, whoever came up with that is clever. I would have never come up with that on my own.
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Some security camera systems have this built in. They show snapshots of various times where you choose the total period, say 24 hours. Then you glance through the snapshots that are all displayed at once on the screen and click on the last one where your bike was still there. That will then “zoom in” the timeline and show another set of snapshots, though this time within a smaller total time window. Keep clicking on the last panel with the bike, and it will soon show you the clip of the bike being stolen.
Really helpful to find out when something changed.
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What if you had to guess a number between 0 and 100 and the other person (or an application) only told you if the number is bigger or smaller? That's the form that's usually presented to CS students and most people end up figuring it out on their own. Then the trick is knowing how to generalize it.
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waves magic wand computer science!
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Honestly you probably do it already without thinking about it when trying to figure out where you left off a video that you never paused.
Or if you ever had VHS tapes, or so e from of disc media... perhaps a cassette when looking for a particular part of a song.
Maybe not as methodical as perfectly breaking it down into halves of halves, but xlos enough to help you pin point what part you are looking for.
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Works the same for finding a burned out bulb on a string of Christmas lights too.
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Without binary search, we would not have search engines today
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Jesus fucking Christ, I know police are dumb, in fact if your IQ is too high you can actually be legally barred from employment as a police officer in the United States of america. Look it up. But fuck incompetence of these Jokers continue to tickle my asshole in a negative way
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I fuckin hate cops as much as the next person but people love to spout this fact, but there is literally only 1 police department ever that has been documented doing this, and it was the one police department in Connecticut.
However the court did in fact rule it was legal, yes.
But the way everyone talks about it you'd think this was some super widespread policy that many departments use. And as far as I can tell there's only ever been the 1 example. It's the same case that every single article about it refers to.
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The final project in my instrumentation class was to tune a PID controller for a hot/cold mixing valve. I (CS/ENG) was paired up with an engineering student and a lot of it was throwing parameters in, seeing if weird shit happened, and then turning down or up based on the result. I had a programming final and something else I was supposed to be studying for, so I just started doing a binary search with the knobs. We got the thing tuned relatively fast and my partner acted like I was a wizard.
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How do you do a binary search for an open-end scale (are PID params open-end?) and three knobs at the same time when they interdepend in their influence? I need to know since i have a PID tuning on my personal projects plate
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It's been ages, but we'd done rough calculations for the three controls so we roughly knew what we needed. Our teacher was big on manually tuning instead of just using formulas since he thought just running numbers "lacked artfulness."
So we grabbed a point and started searching around manually. I think we were just tuning the derivative portion at that point, trying to get a fast response without the system without it going chaotic and noisy.
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Oh yea this is how I managed to convince our building management company to identify bicycle thieves in our communal garage.
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This is how I look for the best bits in porn
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Fast forward half way and see if the woman is still there?
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I fast forward half way and pray she still isn't slobbering on some knob at that point and they've gotten down to businesses already.
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It's got huge amounts of applicability in many lifestyles and situations that most people never realize until the moment arrives. I once played a fun game that had you guess a number between 1 and 1 Billion with them telling you higher or lower to earn your freedom. Takes a couple of minutes at most.
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A police officer being unable to think in such a fashion is exactly why no one could solve the see-saw riddle on Brooklyn 99.
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For those looking for the handout:
person: A B C D E F G H I J K L
round 1: L L L L R R R R — — — -
round 2: L L R R R — — — L R L -
round 3: L R R — — L R — L L — R
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Where is the piped bot when you need it
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You can just replace the domain of the url with
piped.video:
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How do you solve that? I saw a solution in the comments where it says to start with numbering all the people and butting 1234 and 5678 on the see saw, then it says if they weight the same then continue and that seems to work. But if they dont weigh the same it doesnt work and it doesnt say what to do in that case.
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acab
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all cops aren't binary-searching
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that dawn of humanity is only going to work if the rewind/fast forward is instantaneous.
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Also, if I rewind to the Neolithic and I see a bunch of cavemen, sabertooth tigers and a Schwinn chained to a bike rack, I'm not going to just fast forward from there. I have other questions.
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I mean... You're not gonna outrun that sabertooth on foot.
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They're paid by the hour.
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"Yes, chief, I'll need 72h to manually review all 72h of footage and cannot do any other activities in the meantime."
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I'm realizing now that this would have been super useful when I worked in Loss Prevention way back when. Wish I had known...
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Even without algorithm knowledge it should be fairly obvious that you can just fast forward several minutes and check if the item has gone missing.
Not the most efficient solution, but beats watching the entire tape in real time.
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You can now go back working there with this new secret technique.
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I mean, in the era of VHS this won't work because ultimately you're fast forwarding and rewinding. So you're gonna watch it anyway. but in the digital era I thought this would be what any Police officer did?
Like... they're not even gonna spend 10 minutes on a theft?
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my guy half of them don't spend 10 minutes on a murder. There's a reason it's called detective fiction
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Like... they're not even gonna spend 10 minutes on a theft?
What and be responsible for paperwork?
Cops are the biggest bludges you’ll ever meet.
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In Artillery you call it bracketing/straddling.
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For anybody else looking for the source of this quote: https://archive.md/RyZI0
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What are we supposed to believe this is some sort of magical VCR?
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Most security cameras record mpegs to hard drives
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I used to do this when having problems while rendering video in my past life.
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image transcription:
Afterwards I found a chatroom thread among Cambridge computer scientists, one of whom had also been told that unless he could pin down the moment of theft no one would look at the footage. He said he had tried to explain sorting algorithms to police - he was a computer scientist, after all. You don't watch the whole thing, he said. You use a binary search. You fast forward to halfway, see if the bike is there and, if it is, zoom to three quarters of the way through. But if it wasn't there at the halfway mark, you rewind to a quarter of the way through. It's very quick. In fact, he had pointed out, if the CCTV footage stretched back to the dawn of humanity it would probably have only taken an hour to find the moment of theft. This argument didn't go down well.
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This sparked something magical OP.
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And I had worried about it being a picture of text.
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I was in exactly this situation. My bike was stolen, there was CCTV, they said it would take hours to go through the time during which it was stolen.
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"Can I have a copy of the recording?"
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That's what I said, and they said no
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Source article for the curious, and an unpaywalled copy on archive.is
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Pfft, didn't even try to enhance the footage. They're obviously not cut out for forensics work.
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This post is horrifying, not funny.
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That's a search algorithm, not sorting
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This student should never go to xitter. Or will be canceled instantly.
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Sure, fuck xorg knockoff. What's the connection here, tho?
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Binary search. They don't like it.
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Wtf are you talking about?
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Binary search
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everyone is a little bit gay!
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I do not get why it would work in that case. I assume the scenario is someone with a bike coming, doing theft, then leaving with the same bike.
Therefore there will be a period without bike, then a period with bike, then a period without bike again.
Let's assume there is no bike on the particular moment viewed. How do you know whether it occured before or after the theft? If you make the wrong decision, you get stuck on an endless binary search.. Unless you take note at each timestamp where you made the decision, draw a tree of timestamps, and go back the tree if your search is fruitless but that's much more complicated than what this post says.
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To me it sounds like they stole the bike.
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Thanks indeed I misunderstood the problem
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You're making this way more complicated than it actually is. The guy definitely can give estimates for when he parked the bike and when he found out that it was stolen. It's not that complicated.
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I misunderstood the problem. I thought the thieve came on bike to steal something. I did not get that the bike itself was what got stolen.
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I get the sentiment, but you want them to waste public resources doing it on all these different clunky uis and software? Sometimes these take minutes to load new information to parse.
Maybe waste your time pinpointing it instead of expecting public resources to do what you could do for them?
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I mean... their job supposedly is to protect and serve the citiens so yeah... I'd expect them to use their tools to do their job.
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So I should do their job for them?
Why the fuck are we paying them then?
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on all these different clunky uis and software
As someone who has used security cam software before. I swear they are designed to be as unhelpful, slow, and convoluted as possible.
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That’s an interesting way to say that they shouldn’t get paid if they’re not doing their jobs. 
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Yeah, every time I have ever had to hand over footage to the police for thefts at our family store, I clip and organizr that shit. I also include a paper identifying each file, the timestamps and what happened during them, any details I identified that they can corroborate (physical description, identifiable clothing/tattoos, make and model of vehicle, license plate number, etc.). I often end up putting in 1-2 hours of work on it watching, editing and transferring footage.
If you want traction and results from the police, you need to make it as easy as possible for them by doing the heavy lifting yourself. The cynical view is that thats because they just don't care, but also, in fairness, your case is one of dozens of cases on their desk and the cases never stop coming. This is your priority, so put in the effort instead of expecting others do so. That being said, that is much easier when you have direct access to the cctv footage. I'm guessing this student didnt.
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410 comments