Already what you might have forgotten about were things that you know we struggled with in the past. And as usual, we can do 30 minutes of that, just a bit of theory, and then 30 minutes of leak code. How does that sound? Yeah. Okay, so if I say what is a word? What's a word? Say malware. I mean, it's not malware, but it's. Propagates through the Internet. It's a piece of program. Yeah, that's the key points here. Gets. No, sorry. Sorry. Can you? You're almost there. That's why that's why I stop talking you. There's a key point to it. It's self replicating. Replicating. So that's obvious, right? But this will usually count for one points when they ask you, Oh, what's a worm? So just to keep that in mind, what's spwear? It accesses so malware that access is like your what you're doing on the screen, your interactions Oh wear to spy Yeah spy interactions interactions in the objective of like stealing past forthem to another Yeah. Your passwords or money. Yep, what's fishing? Fishing is setting up a fake website or a fake information gathering thing to get personal information. What's the difference between fishing? Yeah I got a personal info. So this will usually be like a text message or like one of these really corny like Oh, redeem your free gift card or something like that that you'll get like as a message. And what's the difference between fishing and farming? I forgot. Sorry, no worries. It's a bit nuanced here because they're kind of basically the same thing, both fishing and both forming. If you hear or start seeing a ph somewhere, it's a steel data. So I'm going to make a little grid fishing. Informing. The basic way to think about it is if you're fishing, you know you're not putting in much effort. No, you're you're just sending like spam like spam calls, emails and you can detect it via something like you know misspellings. Right or AI like you you can see like an m dash in there is probably not going to be a real email, right? Whereas in farming it's a bit more targeted. So it's it's targeted. So Yeah, let's say you want to hack into Google for some for whatever reason and you send, who's the secret CEO of Goole's? Tim Cook? I don't know if he's the CEO, but let's say I don't know, let's say you want to hack into SpaceX or or Tesla and you send an email to ion musk, right? And you're like, Oh, you know this email and you make it look legit, make it look like a company email. And then this the websites you might click on, right? You might have like a website and that website that they click on would be like a fake, right? And then theyclick on it, theyput their password, and then suddenly you've got Elon Musk's password for his bitcoin account and you're a very happy man, but you know not him, he said. So basically, it's kind of a more targeted way to steato steal money and information. Yeah. All what's a dos attack? It's when a computer sends corrupted or or information to try to overload a server yewhat they stand for. Denial of service, yes, was. How do you say the word again? Distributed denial of service. Yes, exactly. And what does that mean in practice? It's a malware that's sent to many computers to do a doos attack. Exactly. Very nice. They all, they all, at the same time, hit the same server. So it just goes down. Okidoki, all right. One of a bit of a boring one. What's an ide? Integrated development environment and what's the advantages of an ID. There's many built in adons functions to use. It provides a. Easier to set up the environment, easier to code. More efficient to code in and more efficient. Very nice. What about disadvantages? Any think you no, I mean. Like han Yeah there's not that many. The main one is that you know it's bulky and slow, which you don't really need that much setup for like a small project. Another one, 21, you can Yeah you can exactly can get a lightweight one. So that's why there's not that many disadvantages to it. But basically, Yeah if you have an ID, it just makes it easier. You know you can also have I'll just a few of them. You also have like debuggers where you'll have like interpreters that will like highlight code. So I don't know if you used an ide before, but you might create a new variable like x and then you never use x so it like there's a squivy line underneath it to tell you like, Hey, you haven't used this bar able here. So Yeah, there's a lot of things you can say but Yeah, just wanted to test you out on that very nice. What's inside of an ip packet? Or firstly, what's an ip packet? It's a packet of data sent over the Internet to a receiver and what's inside of it. There's the data, there's the ip of the sender and the receiver. Yes. Can you think of one more thing? Metadata yes, metadata. That's a good one. That's a good one for for metadata here inside of it, you might find something like ip number. So for example, ipv six or v four, v six slash v four, or you might also find like the the number. So ip number would be like, Oh, this is the fourth ip packet I've sent to you or something. What about tcp? What is that? It's a transmission protocol. You send a file with send an ip package with an acknowledgement, and you don't send another one until they send back an acknowledgement or if. Or if it's a runtime error or something that they have and you're just gonna resent the whole thing exactly red. So it's pretty much exactly what you said. You have just to to say what you what you said already. In other words, you have the sender, a receiver b and a sends a packet and b says, okay, I got it. And then once a set and boom, he sends a packet, b says, okay, I got it. Sends a packet, okay, I got it. And here it looks like it's cereal. What does cereal mean? Cereal like this. In order Yeah exactly so. No, nothing. Sorry. No, no worries. You question. But because I was gonna say you can you can do it serially, but you're not actually doing it. Seriyou can do it in parallel, right? You can send several packets before b confirms and then b can say yes to each of them individually. So you don't have to actually do it serially. You can just do it in parallel. Okay, very nice. What is all right, let's go to browsers. What is ssl? What does it stand for? What does it do? I don't know what about what it does. No, sorry, I don't know what if I say certificate? Is that right? Yeah, it gives you when you enter a website, it's gives you a certificate that did is the write websites and not a sort of hijacks website. Very nice. And how does the flow work? Like how how does it work if I go to a website right now or if you were to go to a website, how do you how does the flow work between you entering the website and then getting like a certificate, making sure it's the right one? You go in the website, you send it link or address of the website to the to. The server that has the certificates and it will check in its list if the certificate is of that link is there, if it's not at all sent back that it is not safe to enter that site. And then. Basically, you forgot one small thing about that. It gets to certificate through the site. So site sends back the certificate and this is called the certificate authority. So basically, you've basically got it. Just remember that ssl is called secure socket. Layer and it kind of this is the protocol, right? You send the link, the site replied for the certificate, you get the certificate, then you look in your own repository of certificate authorities, you're like, okay, I'm going to ask certificate authority if this is a good website, if I'm being, you know, if this is gonna to be dangerous for me getting on there and then you ask certificate authority and the registry will say either yes or no and then if it's a no, you'll actually get a page on a prome. You might have seen it before. It says this website isn't secure, right? And it looks like you can't enter a website, but all you have to do is Press advanced and then proceed anyway. So you can still go on those websites is just a way to protect users. Okay, very nice. And just to kind of complete this, the site here, I've actually done this myself. The sites here will basically, when they first create their website, theygo to the certificate authority and theysay, Hey, my name is, I don't know, John, right? My name is John, and I wanna set up a certificate for this website. And then what you'll do is you'll send the detail, you'll send your email address, you'll send your ip address and then the registry will say, okay, that's your that's your website and then itreply back with an, okay, and that's it. And then basically they will store your certificates and then now can you can access it safely and you need to renew this every month. But you don't know. It's not that important for you to know, but you do need to do this every month. Key, don't key, all right? Okay. You've had a few troubles with this one before. Okay, what do I have to do? All right, so please get out your pen and circle. Will me the primary storage types in this in this list of things you have to give me the permission to my bad. I'm just that's you right now. 一个。The primary storage types. Sorry, I forgot, primary is the one that. Is that keeps data within itself, even nothat runtime. You tell me I'm being cheeky. I'm sorry. Yeah, I'd rather not tell you and see if you remember or not. From httssd magnetape. Okay, so I see what you went for. Unfortunately it's not correct so I'm gonna regive you the definition. Primary storage is a type of storage that is directly accessible by the cpu during runtime. So okay, if youmind maybe I can help you deleting these and trying again. Oh it very nice. Okay, you've got it. And trying again and seeing if you can if that changes your answer. This is d and hhd are accessible, right? So almost you're halfway there. In fact, these are not directly accessible by the cpu. Actually. This is really, really interesting and I wish I could teach you about this, but it's just not in your curriculum. But the way we access httD and ssd is done by a separate component called a drive access or or something I forgot, but it uses a very cool algorithm. But yes, it's not for this kind of class, but you're you're basically there, right? These are secondary storage types. They're secondary because the cpu can still access them. Adjust would need to go through this whole like process, but it's not directly accessible by the set, by the cpu. However, this is good. This is good. This is good because basically the cpu ram is while it's not really there, usually this four level, so ram is a bit further away. Ram is considered to be directly accessible directly in memory because it's super easy to just go get computer can just go get it. And what's by the way, what's the difference between ram and ram? Read only and random random access. Yeah what does that mean in practice? You can only read from a ram, ram, which means it's pbuilt as a ram. You can store and read any data exactly. And now bonus question and see where is the heap in those? The ram, exactly. The heap is in the ram. Yes. Rom is just used for startup or like bios setup, things like that. And a key point is that it persists even if the computer switches off was as ram is no more electricity, no more storage, it just turns off. Great. Okay. Now would you mind removing the I don't know how you did that so quickly. You just select one. I see three, select tool and then you just select and remove. Nice. Nice. Okay. You're you're quicker than me. Okay. Now tertiary tertiary types, tertiary storage types. Would you mind circling the tertiary types? Ps, now there go. Yep, that's perfect. Secondary types. Okay, I'll remove those ones. The usb is also a secondary type. Usb is also Oh, that's a good question. Good question. Yes, wait, let me get your syllabus out, because they can can be tough. Most of these definitions are done by cie. So they're not like they're not global. But yes, hdd and ssd are indeed are indeed storage secondary storage types. Would you now please order one to the last number? So one being the fastest and then n being the slowest, order how fast each of these. And usb is a secondary storage device. Perfect. Yes. These two here. I would have forgiven you if you had said 23. As you know, they're they're quite similar in terms of access speed. So this is perfect wherever you see registry like ldr, R, cash, Yeah exactly. Cash, right. Registry will still be quicker than cash always. Why is that? Why is registry quicker than cash? Just closer to the cpu than even cash? Yeah, exactly. It's closer. And we already know what's inside the registry. We don't know what's inside the cash ache. You can have a cash mesthe, cash miss, right? If you try to get something from the cash ache and it's not there and you still need to find the item, you need to run a hashing algorithm, whereas a registry is just right there. So registry is always a fastest, very, very nice, okay, a big improvement from from last time we needed this question. So I'm quite confident that if you see this, you'll be you know you'll be feeling a lot more confident about this. Great. Any questions so far? No. All right, let's do maybe one more before we go to leap code. Do you if I were to say, if I were to ask you what is the Universal Serial Bus, what would you tell me? The data bus. What does it do? It connects, it allows transfer exchange of data within the cpu. Yes, exactly. And if I were to tell you, if I will, like if I have a 64 bit computer, right, 64 bit architecture computer, the wilength would be 128 bit for the bus. Yeah 64 bit then it's also 64 then exactly. Exactly. That's a that's a common a common gotcha. But if it's a 64 bit architecture, then 64 bit bus, otherwise it's 32 bit. Why does that matter whether it's 64 or 32 bit? It matter. Depenif you have a if you're on a 32 bit architecture and you have a long, long int ch, which is eight bytes, 64 bits, you're going to have to take two cpu calls or two clock cycles to even send that data. That's a perfect answer. That's a perfect answer. Not only that, but you're going to have an increased cash acsize, right? You're going to have an increased well ram access because you've got pointers. Your pointers will not be 64 bits long, which means you have not double, but two to the power of whatever. 32 will be six or five more. You can also have more ram and you can also have more Yeah, exactly. So you totally understand there. And so that's why it's so important. You can just access things right? You've got more heat, more memory. So 64 bit and 64 bit is kind of the limit. It's got 128I think for like supercomputers. But like if you're doing more than 64 bit, then you know maybe nasa is doing that, but not not many people are. That's the bus. Quickly before we go to lecode de, I'm just going to ask you to draw me a cpu architecture here. Detor, Yeah, there's. See you to the. There's an accumulator somewhere near it. There's ram above, but not needed. There's cash. This the. Hil, you? I think that's all you need for a basic cpu. There's some things that are right, there's some things that are missing. But globally, I can see you've got the idea here. Let's add a bit more to your cpu. So you said there's a Universal Serial Bus. What other types of buses are there? Maybe don't maybe bus. There's a bus for the ram. It's everything that connects. All of these are one. The webhas a separate bus. What's the bus that connects all of these from the cu? Data bus control bus control bus. In actuality, you have three different types of bus. You have the control bus. This one, you have the address and the ram. Yeah, exactly. Bus and you have the address. In reality, these two are kind of interchangeable, but they basically will ask you the three data buses, well, data address and control. Remember, for the cu, ram is gonna to be in the same category as ram. So you wanna move that out somewhere here, right? And have it like this. Just a conceptual thing when talking about how detailed we can make a cpu, there's actually quite a few ways to make a cpu. So I think next class, what I'll do is I'll bring a schematic, and we're just going to try and ingrain you know what what cpu it is. But rule of thumb is you've got the accumulator down, which is perfect. You've got the control unit down, which is absolutely critical. You've got the cache, which with A C or just cache like this, these are the three and and the althese are the main things. But there's also the memory data register, the mdr, the memory address register, the maand. Then you also have the pc, the program counter, the accumulator. Remember, it's just a register to store what happens inside of the alu nif. One more, you have the instruction register, the ir, right? And then your schematic here is kind of correct. Wehave to do it with a bit more detail here. But youhave like a little box around it. The alyou would be inside that box and then youhave like some kind of data and address bus with the ram, right? So youhave it youhave youhave basically a bus that connects all these things. This would be like the data bus plus address bus, right? That would be 64 bit. If it's like a if it's like a 64 bit computer and then each of these right would have like. Each of these would kind of connect to the cu in a certain way with an independent bus, which would be the control bus. And so Yeah, they would be on and off the bus. And there's like a coordination algorithm based on the pc, the program counter. And in reality, when I was learning how to build, you can build your own eight bit computer, but when I was learning how to do that, the program counter has like a big and gate with every single components in the computer to be like you can run or you can't run because it's to do with the way the electricity moves through the exactly the clock. Okay, I'll I'll stop planning ding, let's let's let you share your screen. There we go. Already on leak code. I don't see the little star for the favorite on the top right now. I'm joking. Let's do. I don't know. I'm joking. I'm joking. I'm joking. Let's let's go for an easy one. Warm up slow. But I think we're getting ready to do our first hard one, a first medium one. But let's let's do a medium. So if you actually scroll up, there's a way we can filter these. If you go to on the left there you've got like a filter icon. And here you can say difficulty is easy. Very nice and Yeah, let's have a look. Okay, okay, and scroll down. Go climbing stairs. I think we did that one together. Yeah, we just did that one. Yeah. What else? What else about battree? Maximum depth battree tree? Oh, this one, 121. Best time to buy and sell a stock. It's a good one. Okay. Do you see what a stock is? Yeah, cool. Okay. Then I won't give you too much detail. I'll let you read it. And then once you've once you've read it, let me know what you think. And and I can kind of give you some more context if you need it. But if you feel confident and you can just kind of start going at it. Okay, I'm thinking you just propagate through the you just find the max, get them in and then find the max. Okay, what about though? If you have a situation like this, imagine this is your stock, imagine it's going like this and then it goes up like and then it goes like this. Would your algorithm still work if the stock was like this? Mean you would find the two differences. So youfind, this one would be the one here and here, and this would be the min, and this would be the maximum, right? Yeah. I mean, it would propagate through and find them in. I see, I see. So basically, okay, okay, wait. So youbasically do youonly find the youonly find the max after the mid right is what you mean. Yeah but if you have these, I think I could add just get the first one and then get the second one, calculate the profit and then continue on calculating. If that second one is lower than the first, I would change the variable to store the second one. Very, very nice. Very, very nice. Okay, I'll let you I'll let you write some code. Is there any limit on the size of a like the size of the price? I think you might nah, I don't think there's a limit. Maybe it takes the crassive. Go on. I try, then. Wait that wait that size. I'm going to get myself a glass of water, but you seem to be on the right direction, so I'm just going to let leave you code. I'll be right back. Nice. Oh, wait, I muted you tonight. I did not mute myself okay okay. Very nice. I think you've got it, but there's something missing here. Yeah, I have to calculate the remaining thing, but. Is that it? Almost there. Give it a run, though maybe I'm wrong, think it sort way and I need to lock in again. Okay, so close what happened here? So before we keep going, before we keep coding, try to explain to me in your words, what your strategy is to try and find the maximum profit. I'm going to first find the first minimum and then if I it is that minimum, then on the next try, it would try to find the difference. So basically what you're doing, let's say you've got a stock like this, I wait, I need a last profit or something. I think I need a last profit to restore it. And in comparison. Then I need to initialize this. Yeah, it works. You got it. Hey, let's go. Very nice. Let's see. So. Close. But what happened there? It seems so let's let's have a look at. At. What could happen here? If I look at your code, last profits for entire in size if min prices. So if you find a min that's less, then for example, zero here, we don't actually initialize last profit. So it could be any number. But let's say it's a very large number, then what we do initialize, where do you initialize here? Prices is Oh, you're right. So last last price is equals profit. So if min prices is less than min, so basically you just keep going down, right? So let's say you've got let's say you've got a graph line that looks like this, right? Keeps going down. So you keep going down. And so you reach a minimum here. Then if you found your minimum, then you just last profit. That's profit. Profit versus profit, when it's mint, you start going up. But once you start going up, you say profit equals here and you just say, profequals presses I minus min. Yeah. So because it doesn't change. Yeah. Yeah, exactly. And the profit will just be this change here. But here then you say if last profit is greater than profit, then profit equals last profit. But then here you so it's quite close. But you say price last profit equals profit, which you're just saying, Oh, it's the current profit now and then you're reassigning profit to be pressed I management as so you're only going to ever have that maximum difference there if that makes sense. And I just want to before we keep going, did that make sense? What I said? Yeah, Yeah. Okay. And the problem with that is that you'll never find the the change in price. So I want to propose something a bit different because you're you're halfway there. Well, you're 90% of the way there really. But think about think about this again from a more like abstract perspective. So if you go back to the description of the problem on the left hand side on the problem list, and I think I know like what mistake I made, it's if there's like a. One, 27. And then there's a three end like. 15, I just do wait. We know that still counts, right? No one, 27 is run. Let's see if men is good. Purses continue. I think this should work, though I don't know why. Good. Last profit it. You can click on the used test case there on the left with the wrong answer. And Press the run button now. And now you should be able to see if it works for that test case. No, I don't. It's the same code, but I just can't figure out why it doesn't work. Let me try to really delve into why preson, because I'm thinking of a different strategy in mind. But but I just want to understand why this code isn't working. Less profit profit just one for into I size. If min is greater than price is I than you keep going down. Otherwise last profit equals profit. So you say the last profit equals the current profit and you say current profit is profis I minus min. So the last minimum. So you're trying to find the last minimum with a new maximum. And if last profit is greater than profit, well, you should really just add. Profit plus equals last profit. This should always be positive anyway. It should never be negative, right? Because you will, you already checthat. There must be. So you must say profit plus equals less profits. Hope this goes wrong. It should be equals because it I mean, my thought process was that it it was bigger than it would reset. Would fall back to the last value. I see. Okay. But think about it this way, right? If you go back to the description of the problem, they're on the left up near wrong. Answer a bit more description. It says you want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit, return zero. So you want to find the biggest difference between min and max. What you could do. So you're you're basically doing this already. But what you can do is you can say if you if you have this graph, for example, here you go through it and here you've already got it right? Min is less is greater to them. Press ses. I so min is precise. So you're going down. We reach a maximum. We start going up. If we get too high, if we start going down again, we store that into a variable called max profit. And we start going down again, and we get this new minmum, new maximum, and then we say, Oh, this difference diff. Is it bigger than max profit? And if it is, than max profit? So that's kind of what you did over here. Yeah. But I think mine doesn't need that new calculation, just goes here down. It calculates every profit here until here the new minimum is reached. And then it starts going up here. It stores the new profit. And if it falls, it falls back to that profit. And as it goes up, it stores itself because it greater and then it goes to the top. And then once it falls because profit is less is it falls back to the last profit, which is here, which is the main one. Yeah but I'm wondering if that could fail somewhere in the future. Unsigned for int, I equals one, I equals a zero. No, no, because min is already set to zero. You're right. I equals one size. We say min equals Press ses. I. Profit equals price is I minus mbecause? We're kind of rolling that behind us. Profit that profit, it was profit. Proequals price is five us. Should I do that only if profit is greater than profit last profit is set. I feel like the problem with this line of code is that we're resetting every time. Yeah. So because if you're going back, so when you're going down, it's very it's very obvious that you're going down, right? You're going down and you're just saying min equals price is I and then you just keep going down. And then once you've set min price, you see profit equals price is I minus min, but you're resetting it every single time, right? You're basically saying every time you go up, that's your new that's your new difference. So instead of doing a new difference every single time, you want na find a way to add that up. You want to find a way to do nothing until you get to the maximum. And then once you get to the maximum, then you put profit equals Press min or max minus min and then that will be your total profit, right? Instead of this would be the same though as this. I'm not I'm not convinced because here what we do is we say last profit equals profit. So we take the last profit that we made and we say it's just equal to profit, which minus one at first I think I know why this failed. Okay. And that should work. Oh very nice. It's a TypeError. I didn't even realize. Wow. Okay, I'm actually kind of stumped. How did you fix that? I changed from char to short. No char max is 127 and so wereach 127 and just return that. Yeah, okay. I even spot then it falls back, then it overloads to the negative and then it's just gonna return that because last profit is always 127. That makes so much sense. I hadn't even realized that. Henry. Good job. Good, good job. We have we've ran out of time, but this is really fantastic to watch. Man, you've really improved and I think I think you're quite good at these problems. I mean, this is a great example of it. I didn't I wasn't even able to debug your code, right? So honestly, let's see if it works in the submissions. Nice. Yeah, very good. So honestly, hats off to you. You did some great work today. Great start of the year. And if you're still up for doing these kind of leak code problems, we can keep doing that if that's what you're interested in. I'm not sure what you think about that. Yeah, I think it's good. And Yeah your C++code are really is really good. I almost think that we should start start doing it in Python not only for you, but also for me so I can follow what's going on because my my C++, as you can tell, I didn't even realize there was a type issue. But but Yeah, great job as usual. And you know let's do something similar. Next lesson. Okay. Does it translate it? No, Yeah, unfortunately not. But I'm a lot more that that's Python. The difference between these two though, Yeah says Python two and Python three. Python two is old and we don't really use any more. Python three is typed as well now, but Yeah type ped c. You've got a list precishes, but it's like loosely typed. It's kind of interesting. But I'll be able to help you a lot more with Python because I actually know a lot of Python, whereas C++I coin it, but Yeah, I okay, great job. Great work and have a nice rest of your holiday. Thank you. Bye sir. You too. Bye bye.