Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated: 1 00:00:00,390 --> 00:00:05,340 Hey guys. So I've got another code challenge for you. And this one, 2 00:00:05,790 --> 00:00:08,970 as the title suggests, this is a difficult challenge, 3 00:00:09,120 --> 00:00:13,380 and this is something that I expect some of you might need to spend 15, 4 00:00:13,380 --> 00:00:17,460 20 minutes on. Others might need to spend 30, 40 minutes on, 5 00:00:17,820 --> 00:00:22,290 and it might just be something that you need to have a think about, get stuck, 6 00:00:22,620 --> 00:00:25,920 come back to it after a bit of a break or sleep on it, 7 00:00:25,980 --> 00:00:28,650 come back to it the next day. It's not easy, 8 00:00:28,890 --> 00:00:31,530 but what I'm trying to say is really, 9 00:00:31,530 --> 00:00:35,310 really give it all you have before you check the solution video, 10 00:00:35,790 --> 00:00:38,940 because it's a really, really interesting challenge. 11 00:00:40,020 --> 00:00:43,710 So the idea is that we want you to write a program that works out 12 00:00:44,070 --> 00:00:46,980 whether if any given year is a leap year. 13 00:00:47,670 --> 00:00:50,400 We know that a normal year has 365 days, 14 00:00:50,490 --> 00:00:53,340 but leap years have an extra day in February. 15 00:00:54,060 --> 00:00:57,750 And the reason is actually really, really interesting. If you're interested, 16 00:00:58,110 --> 00:01:02,550 there's a really good explanation of how leap years work and why we have them at 17 00:01:02,550 --> 00:01:06,780 this YouTube link. So just go ahead and copy this URL and check it out. 18 00:01:07,530 --> 00:01:11,160 Now, the way that you work out if a given year is a leap year, 19 00:01:11,250 --> 00:01:15,030 so let's say we pick one out of thin air, 2020, 20 00:01:15,570 --> 00:01:19,980 is that on every year that is evenly divisible by four, 21 00:01:20,130 --> 00:01:23,760 so that means divisible by four with no remainder. 22 00:01:24,480 --> 00:01:28,170 Then that is a leap year, but except the years 23 00:01:28,230 --> 00:01:31,710 that is also evenly divisible by a hundred, 24 00:01:32,640 --> 00:01:37,560 unless the year is also evenly divisible by 400. 25 00:01:38,100 --> 00:01:43,050 Now 2020 divided by four is equal to 505. 26 00:01:43,380 --> 00:01:47,520 So it's evenly divisible by four. There's no remainder. 27 00:01:48,480 --> 00:01:52,560 But the rule says that even if it's divisible by four, 28 00:01:53,130 --> 00:01:55,920 if it's evenly divisible by a hundred, 29 00:01:56,250 --> 00:01:59,040 then that is still not going to be a leap year. 30 00:01:59,340 --> 00:02:04,340 So let's try that 2020 divided by a hundred equals 20.2. 31 00:02:05,550 --> 00:02:09,540 So this is in fact not evenly divisible by a hundred. 32 00:02:09,990 --> 00:02:14,970 So that means it is still a leap year. But then it says 33 00:02:15,180 --> 00:02:19,560 unless the years also evenly divisible by 400. 34 00:02:20,310 --> 00:02:21,210 So 2020 35 00:02:21,210 --> 00:02:26,210 divided by 400 is not evenly divisible. 36 00:02:26,790 --> 00:02:29,970 So it is in fact, still a leap year. 37 00:02:30,870 --> 00:02:33,990 The trickiest part of this entire challenge 38 00:02:34,020 --> 00:02:39,020 I would say is getting your head around these three sentences: a year that is 39 00:02:41,310 --> 00:02:45,570 divisible by four with no remainder is a leap year, 40 00:02:46,080 --> 00:02:50,160 except if it's also divisible by a hundred. In that case, 41 00:02:50,160 --> 00:02:51,360 it's no longer a leap year, 42 00:02:51,960 --> 00:02:56,960 unless that year also happens to be evenly divisible by 400 then it is still a 43 00:02:59,440 --> 00:03:03,220 leap year. What I recommend doing is a) 44 00:03:03,610 --> 00:03:05,860 if English is not your native language 45 00:03:06,220 --> 00:03:10,060 then have a look online for the rules for determining a leap 46 00:03:10,060 --> 00:03:13,990 year in your own language, because these words, except 47 00:03:14,020 --> 00:03:16,660 and unless, are so, 48 00:03:16,720 --> 00:03:20,950 so integral to how this algorithm works. And you really, 49 00:03:20,950 --> 00:03:23,530 really need to understand exactly what it means. 50 00:03:24,970 --> 00:03:29,970 Then what I recommend you doing is to go ahead and create a flow chart, 51 00:03:31,150 --> 00:03:33,820 just like what I've done in previous examples. 52 00:03:34,210 --> 00:03:36,730 Head over to a website like draw.io, 53 00:03:37,000 --> 00:03:39,580 or simply just write it on a piece of paper. 54 00:03:39,610 --> 00:03:44,610 Draw it out and visualize what this actually means in terms of your code. 55 00:03:45,820 --> 00:03:48,010 Now, if you really get stuck on that, 56 00:03:48,430 --> 00:03:51,640 I've also created a flowchart for you. 57 00:03:52,090 --> 00:03:55,660 So if you actually get stuck creating the flowchart, 58 00:03:55,840 --> 00:03:58,720 there is one there that you can refer to as well. 59 00:03:59,020 --> 00:04:00,370 But it's a really good exercise 60 00:04:00,370 --> 00:04:04,720 creating your own flowchart based on what it is that you want your program to 61 00:04:04,720 --> 00:04:09,720 do, and your algorithm or your code should correctly tell us whether 62 00:04:10,750 --> 00:04:15,730 if it's a leap year or not a leap year. So it just has to print out leap year 63 00:04:15,760 --> 00:04:20,290 if it is like 2400, and if it's not a leap year, 64 00:04:20,290 --> 00:04:23,230 like 1989, then just print, not leap year. 65 00:04:24,580 --> 00:04:28,510 This is the time to pause the video and really give this challenge 66 00:04:28,570 --> 00:04:32,380 everything you've got. I'll see you back here once you're done. 67 00:04:32,910 --> 00:04:37,910 [inaudible] 68 00:04:40,200 --> 00:04:43,290 All right. So how did you get on? As I mentioned, 69 00:04:43,350 --> 00:04:46,950 this is a really difficult challenge. If you haven't managed to solve it, 70 00:04:47,250 --> 00:04:51,120 then try to come back to it a little bit later on and spend more time on it. 71 00:04:51,750 --> 00:04:56,430 This is a decisive moment. Don't give up on yourself. Keep going. 72 00:04:56,880 --> 00:04:59,760 I'm always going to be here for you with the solution. 73 00:05:00,180 --> 00:05:02,340 You're not going to get stuck. It's really, 74 00:05:02,340 --> 00:05:06,510 really important to try and solve it yourself. Now, 75 00:05:06,540 --> 00:05:11,190 the first thing I mentioned is turning this rule for determining whether if a 76 00:05:11,190 --> 00:05:14,550 year is a leap year or not into a flow chart. 77 00:05:15,120 --> 00:05:19,410 So I've created one which I linked to in the challenge 78 00:05:19,950 --> 00:05:21,270 and it's very simple. 79 00:05:21,540 --> 00:05:26,160 We start off by asking ourself is a particular year that we have in mind, 80 00:05:26,610 --> 00:05:30,870 um, let's say the year 2000, is it cleanly divisible by four? 81 00:05:31,080 --> 00:05:36,080 Which means can you divide it by four with zero remainder? 82 00:05:37,410 --> 00:05:41,940 Well, if the case is no, then it already is definitely not a leap year. 83 00:05:42,690 --> 00:05:46,650 But if the case is yes, then we have to ask ourselves some more questions. 84 00:05:47,250 --> 00:05:51,420 Namely, can we divide it by a hundred with no remainder? 85 00:05:52,170 --> 00:05:56,910 Well, if we can't, then it's definitely a leap year, but if we can, 86 00:05:57,290 --> 00:06:01,730 then we have to check yet again. Can we divide it by 400 with no remainder? 87 00:06:02,240 --> 00:06:05,750 If the answer is yes, then it's a leap year. If the answer is no, 88 00:06:05,870 --> 00:06:10,130 then it's not a leap year. Let's try and code that logic out, 89 00:06:10,280 --> 00:06:14,270 keep your flow chart up somewhere so that you can write your code while 90 00:06:14,270 --> 00:06:15,560 referring to the diagram. 91 00:06:16,430 --> 00:06:21,430 We start off by checking whether if the year that came in through the input is 92 00:06:22,250 --> 00:06:25,280 divisible by four with no remainder. 93 00:06:25,910 --> 00:06:28,790 And you might remember from our previous code exercise 94 00:06:29,060 --> 00:06:33,310 that the way we do this is using the modulo. So year 95 00:06:33,350 --> 00:06:36,500 modulo four will give us the remainder. 96 00:06:37,760 --> 00:06:42,650 So if the remainder is equal to zero, well in that case it's cleanly 97 00:06:42,650 --> 00:06:46,640 divisible by four. And you can check this out yourself in the console. 98 00:06:46,700 --> 00:06:47,300 Let's say, 99 00:06:47,300 --> 00:06:52,300 if you have 8 % 4, 4 goes into 8 cleanly, 100 00:06:52,730 --> 00:06:56,360 there's two four's in an eight. The remainder is zero. 101 00:06:57,050 --> 00:07:02,050 Whereas 9 % 4, 4 + 4 is 8 remainder 1. 102 00:07:04,820 --> 00:07:09,140 So if the remainder from the year divided by four is equal to zero, 103 00:07:09,560 --> 00:07:14,510 then it is cleanly divisible by four. So in this case, 104 00:07:14,630 --> 00:07:17,630 we'll have to go into yet another if statement. 105 00:07:18,230 --> 00:07:21,740 But if it's actually false, then it's definitely not a leap year. 106 00:07:22,370 --> 00:07:25,730 So the else statement that matches this 107 00:07:25,760 --> 00:07:30,760 if statement is going to tell us for sure that this is not a leap year. 108 00:07:34,990 --> 00:07:39,700 But if it is true, then we have to check the next thing. Is it cleanly 109 00:07:39,700 --> 00:07:41,350 divisible by a hundred? 110 00:07:42,100 --> 00:07:47,100 So we check if the year % 100 is equal to zero. 111 00:07:48,490 --> 00:07:51,130 And if the answer is yes, 112 00:07:51,250 --> 00:07:56,230 then we have to check that year against another question. But if it's no, 113 00:07:56,380 --> 00:08:01,380 then it's definitely a leap year. In this case that will lead to an if statement 114 00:08:02,050 --> 00:08:04,660 if it's true, but if it's false, 115 00:08:04,810 --> 00:08:09,810 then we can simply print leap year because that's what it's going to be. 116 00:08:11,170 --> 00:08:16,060 The final question that we have to ask ourselves about the year is, 117 00:08:16,320 --> 00:08:18,970 is it cleanly divisible by 400? 118 00:08:19,690 --> 00:08:24,340 So now if year % 400 is equal to zero, 119 00:08:24,970 --> 00:08:28,810 well, in this case, if it is true, 120 00:08:29,050 --> 00:08:30,520 then it's definitely a leap year. 121 00:08:30,730 --> 00:08:34,630 If it's false, then it's definitely not a leap year. So, you can print 122 00:08:36,340 --> 00:08:40,840 lear year if it's true, otherwise or if it's false, 123 00:08:40,870 --> 00:08:43,120 then we can print not leap year. 124 00:08:45,880 --> 00:08:46,840 And that's it. 125 00:08:46,900 --> 00:08:51,900 That's all the code that you would need in order to represent this logic. 126 00:08:53,230 --> 00:08:56,610 Now there's plenty of other ways you could have written your code, 127 00:08:57,060 --> 00:09:00,390 but this is probably the most readable. Now, 128 00:09:00,420 --> 00:09:02,250 if you've written some different code 129 00:09:02,730 --> 00:09:05,520 but it still uses these rules to work out 130 00:09:05,820 --> 00:09:08,760 whether if a given year is a leap year and it's correct, 131 00:09:09,060 --> 00:09:10,620 then that's fine as well. 132 00:09:10,650 --> 00:09:13,620 There's plenty of ways that you can solve this challenge. 133 00:09:15,060 --> 00:09:20,060 The most important thing I want you to take away from this code exercise is that 134 00:09:20,700 --> 00:09:25,700 you can turn any sort of logic into a flowchart to be able to visualize it. 135 00:09:27,480 --> 00:09:30,030 And once you've got your logic straight, 136 00:09:30,330 --> 00:09:34,050 then converting it into code is much, much simpler. 137 00:09:34,770 --> 00:09:39,000 If you haven't figured out the logic and then you try to start writing code, 138 00:09:39,360 --> 00:09:40,530 then it's going to be a mess. 139 00:09:40,860 --> 00:09:45,860 So first, get to the stage of being able to create your own flowcharts and then 140 00:09:46,950 --> 00:09:49,260 take those flow charts and turn them into code. 141 00:09:50,520 --> 00:09:52,170 If you got stuck on this challenge 142 00:09:52,200 --> 00:09:54,630 or if you didn't manage to complete it for some reason, 143 00:09:54,870 --> 00:09:59,220 head back to it now and give it some extra attention, because this is really, 144 00:09:59,220 --> 00:10:03,270 really important. It's in these moments, these code challenges, 145 00:10:03,330 --> 00:10:05,580 where you are actually going to a level up as a programmer. 146 00:10:05,880 --> 00:10:07,380 It's not during the tutorials, 147 00:10:07,410 --> 00:10:10,260 it's not during the videos where I explain things to you. 148 00:10:10,770 --> 00:10:13,290 It's where you actually write the code yourself. 149 00:10:13,950 --> 00:10:17,700 I hope you had fun on this code challenge and you managed to complete it, 150 00:10:18,060 --> 00:10:22,050 be it with hints or without hints. On the next lesson, we're going to take the 151 00:10:22,050 --> 00:10:27,050 if statement one step further and I want to show you how you can have multiple 152 00:10:27,480 --> 00:10:30,390 if statements and tests for multiple conditions. 153 00:10:31,110 --> 00:10:34,500 So for all of that and more, I'll see you on the next lesson. 14768