Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated: 1 00:00:00,060 --> 00:00:03,150 All right guys, it's time for another code challenge. 2 00:00:03,180 --> 00:00:07,260 So head over to day 4.3 treasure map 3 00:00:07,740 --> 00:00:11,190 and take a look at what is happening here 4 00:00:11,190 --> 00:00:16,190 first. Notice how we've created three lists here for you; row1, 5 00:00:16,590 --> 00:00:20,970 row2, row3, and they've got some blank tiles in here, 6 00:00:21,090 --> 00:00:23,400 and these were just created with emojis. 7 00:00:23,490 --> 00:00:26,910 So if you just search for emoji, um, 8 00:00:27,000 --> 00:00:29,370 and you come across the list of emojis, 9 00:00:29,400 --> 00:00:33,120 then you can simply just copy and paste them right into your code like that. 10 00:00:33,660 --> 00:00:36,090 So depending on whether if you own a Windows or Mac, 11 00:00:36,120 --> 00:00:38,700 you will see the emojis display a little bit differently, 12 00:00:38,910 --> 00:00:41,310 but it doesn't really matter what it looks like. 13 00:00:41,820 --> 00:00:44,940 All that we want to do is to create almost kind of like a, 14 00:00:45,000 --> 00:00:47,670 a chess board or a map like this. 15 00:00:48,450 --> 00:00:51,830 So we have three rows and then we create 16 00:00:51,840 --> 00:00:54,780 another list that includes all three rows. 17 00:00:55,050 --> 00:00:59,460 So this map is actually a nested list because row1 is a list, row2 is a 18 00:00:59,460 --> 00:01:02,610 list, et cetera. And it's all put inside a list. 19 00:01:03,150 --> 00:01:08,150 Then we go ahead and print it so that we add a new line in between each row. 20 00:01:09,720 --> 00:01:13,020 And the final outcome looks something like this. 21 00:01:13,320 --> 00:01:17,610 So if we go ahead and just run the code, you'll see that we have almost like a, 22 00:01:17,610 --> 00:01:22,590 a chess board or essentially a three by three square, right? 23 00:01:23,280 --> 00:01:28,280 And the sort of way that we're going to navigate this map is by using some 24 00:01:29,430 --> 00:01:33,540 indices. So we're going to say that this is column one, 25 00:01:33,570 --> 00:01:37,380 two and three, and this is row one, two and three. 26 00:01:38,430 --> 00:01:42,120 Now, if you've ever played chess, or if you played chess with a computer, 27 00:01:42,540 --> 00:01:47,490 you will know that the different moves or the different positions are often mapped 28 00:01:47,490 --> 00:01:51,630 out using letters and numbers. So for example, 29 00:01:51,720 --> 00:01:56,340 if you want it to move to this square then it would be b4, right? 30 00:01:57,180 --> 00:02:02,180 Or if you want it to move to this square then it would be h3. In our sort 31 00:02:02,550 --> 00:02:03,870 of 3x3 map 32 00:02:04,230 --> 00:02:08,730 the way that we navigate is first by specifying the column, 33 00:02:08,760 --> 00:02:12,810 the horizontal column, and then we specify a number for the row. 34 00:02:13,230 --> 00:02:14,460 So for example, 35 00:02:14,580 --> 00:02:18,480 if I wanted to place my X, 36 00:02:18,540 --> 00:02:23,540 X marks the spot of my treasure at this particular position, then it is one, two, 37 00:02:25,320 --> 00:02:29,550 2 on the horizontal, so column number two, and then one, two, 38 00:02:29,550 --> 00:02:33,870 three, row number three. So I would write that as 23. 39 00:02:34,710 --> 00:02:35,970 And if I wrote 31 40 00:02:35,970 --> 00:02:39,720 then it means I want column three and row one. 41 00:02:39,750 --> 00:02:43,860 So I want you to mark this spot here. So when you run the code, 42 00:02:43,890 --> 00:02:48,270 the idea is that you should be able to specify a location using that two-digit 43 00:02:48,270 --> 00:02:53,250 system, and you should be able to place an X at that location. Now, 44 00:02:53,310 --> 00:02:57,690 in order to do this, it will need you to review what you know about lists, 45 00:02:57,900 --> 00:03:02,900 what you know about using the index to change a particular item in a list 46 00:03:04,480 --> 00:03:06,430 which you saw in previous lessons, 47 00:03:07,090 --> 00:03:09,880 and the added complexity is here 48 00:03:09,880 --> 00:03:14,650 we actually have a nested list. So lists inside lists. 49 00:03:15,100 --> 00:03:20,100 So have a play around with this code and that's the really important word. It's 50 00:03:20,140 --> 00:03:23,950 play, right? There is nothing that could possibly go wrong. 51 00:03:24,370 --> 00:03:26,200 Just try some different lines of code, 52 00:03:26,500 --> 00:03:31,120 try doing some different things and see if it actually prints out the outcome 53 00:03:31,120 --> 00:03:34,810 that you want, where, you know, when you specify a location, 54 00:03:34,870 --> 00:03:37,210 that's the place that gets marked with the capital X. 55 00:03:37,900 --> 00:03:40,540 Pause the video and try to give this challenge a go. 56 00:03:45,570 --> 00:03:47,700 All right. So let's try and solve this. 57 00:03:47,850 --> 00:03:52,170 So notice how at the very bottom of the code, I've got another print statement 58 00:03:52,200 --> 00:03:56,940 which is going to show us the outcome of whatever code it is we write here. 59 00:03:57,480 --> 00:04:02,480 The first thing we probably want to do is get hold of the input position, 60 00:04:02,970 --> 00:04:07,320 right? We know that input always takes in a string. 61 00:04:07,680 --> 00:04:12,090 So even if we typed 23 that's not going to be the number 23, 62 00:04:12,090 --> 00:04:16,290 it's going to be the string with two and three inside the string. 63 00:04:16,680 --> 00:04:18,090 Something that looks like this. 64 00:04:18,780 --> 00:04:23,780 Now we can use what we've learned in previous days and previous lessons to split 65 00:04:24,030 --> 00:04:29,030 that string so that we end up with a horizontal position and a vertical 66 00:04:29,820 --> 00:04:34,200 position. That way we know, well, which column are they interested in 67 00:04:34,260 --> 00:04:38,010 and which row are they interested in. In order to do that, 68 00:04:38,040 --> 00:04:42,990 we tap into this position. And in order to get the horizontal 69 00:04:43,230 --> 00:04:45,540 which we mentioned is the first digit, 70 00:04:45,810 --> 00:04:50,640 then we go ahead and get the zeroth item out of that string. 71 00:04:50,850 --> 00:04:52,710 Remember the string looks like this. 72 00:04:53,010 --> 00:04:55,260 So the zeroth item out of the string is this one. 73 00:04:55,890 --> 00:05:00,540 And then the vertical is going to be the one at position one. Now, of course, 74 00:05:00,600 --> 00:05:03,480 these are still strings as they stand right now. 75 00:05:03,480 --> 00:05:08,480 We've just split up this two-digit string into horizontal and vertical. 76 00:05:09,030 --> 00:05:13,140 So this one, if 23 was the input would be equal to 2, 77 00:05:13,530 --> 00:05:16,920 and this one would be equal to 3. 78 00:05:18,270 --> 00:05:18,570 Now, 79 00:05:18,570 --> 00:05:23,570 once we've gotten hold of the horizontal position and the vertical position, 80 00:05:23,820 --> 00:05:28,380 then we can go ahead and start specifying positions in our list. 81 00:05:28,950 --> 00:05:31,800 So we know that we've got our map, right? 82 00:05:31,830 --> 00:05:34,110 Which is here, this nested list. 83 00:05:34,920 --> 00:05:38,730 And remember that it contains three rows. Now, 84 00:05:38,790 --> 00:05:41,940 if we wanted to get hold of the first row, 85 00:05:42,480 --> 00:05:44,970 then we would write map[0]. 86 00:05:45,750 --> 00:05:47,640 If we want to get hold of row2, 87 00:05:47,640 --> 00:05:51,900 then we would write map[1] and map[2] to get row 3. 88 00:05:52,680 --> 00:05:55,740 Now remember that this is the vertical position. 89 00:05:55,740 --> 00:06:00,350 So this is the that we're going to be getting hold of. Or in this example, 90 00:06:00,350 --> 00:06:02,780 it would be the number three, right? 91 00:06:02,780 --> 00:06:06,920 So we could say map passing in the vertical position, 92 00:06:07,670 --> 00:06:09,200 but there's just one problem 93 00:06:09,230 --> 00:06:14,230 and I'll show you if I go ahead and print this map at the position vertical. 94 00:06:16,130 --> 00:06:19,520 Let's put in the example number, which is 23. 95 00:06:19,850 --> 00:06:24,850 And you'll see that the problem is that list indices must be integers, 96 00:06:25,100 --> 00:06:28,250 whole numbers, not a string. Remember that 97 00:06:28,250 --> 00:06:32,690 we said these are still strings. So to convert them into integers, 98 00:06:33,020 --> 00:06:36,170 we use that integer conversion that we've seen before. 99 00:06:36,920 --> 00:06:40,310 So now both the horizontal and vertical are integers, 100 00:06:40,670 --> 00:06:44,830 and we can run this code again and see how it performs. 101 00:06:47,800 --> 00:06:51,100 Let's put 23 in there, and 102 00:06:51,160 --> 00:06:53,950 we ended up with the error that we learned about in the last lesson 103 00:06:54,310 --> 00:06:59,200 which is an index error. So it's out of range. So what's going on here? 104 00:06:59,770 --> 00:07:04,750 Remember that in our example where the number is 23, well 105 00:07:04,750 --> 00:07:08,440 then the horizontal is the first number. So it's going to be 2. 106 00:07:09,070 --> 00:07:11,740 And then the vertical is going to be the second number, 107 00:07:11,740 --> 00:07:13,240 so it's going to be 3. 108 00:07:13,810 --> 00:07:18,040 And then we try to get a hold of that particular row from our map. 109 00:07:18,700 --> 00:07:21,850 Now, if we pass 3 into our map, 110 00:07:22,090 --> 00:07:26,710 then you can clearly see what's going to happen. There's 0, 1, 2, 111 00:07:26,770 --> 00:07:28,810 there is nothing at position three. 112 00:07:29,230 --> 00:07:33,250 There is nothing that has been offset from the beginning by three, right? 113 00:07:34,060 --> 00:07:35,500 So that doesn't exist. 114 00:07:35,890 --> 00:07:39,340 And this is why we get our index out of range error. 115 00:07:39,880 --> 00:07:41,770 So what do we have to do instead? Well, 116 00:07:41,770 --> 00:07:46,480 we have to remove one from it to shift it to row three, 117 00:07:46,510 --> 00:07:51,040 because that's really what we're interested in when we're writing this here, right? 118 00:07:51,700 --> 00:07:55,480 We can do the same by substituting the three with vertical 119 00:07:55,750 --> 00:08:00,280 so it'll work with any number. And now if I run my code again, type 120 00:08:00,280 --> 00:08:01,113 23, 121 00:08:01,150 --> 00:08:06,150 then you can see that I get no more errors and it actually prints out a row that 122 00:08:06,430 --> 00:08:09,040 I've selected, which is row three. 123 00:08:09,250 --> 00:08:14,050 Now you can of course change these just to make it a little bit more clear to 124 00:08:14,050 --> 00:08:18,550 yourself what's actually going on here. Let's type 23 again, 125 00:08:18,850 --> 00:08:20,980 and you can see that this is what's being printed. 126 00:08:22,390 --> 00:08:26,770 Now the next step is once I've gotten hold of row 3, 127 00:08:27,250 --> 00:08:30,940 how can I get the horizontal tile? 128 00:08:31,420 --> 00:08:34,780 So the horizontal tile we're interested in is the second one. 129 00:08:34,810 --> 00:08:39,250 So it's actually this one. So when we write 130 00:08:39,250 --> 00:08:42,940 23, then it's this tile that we're interested in. 131 00:08:43,960 --> 00:08:47,080 So instead of printing out this row 3 132 00:08:47,110 --> 00:08:50,380 which we selected by writing this code, 133 00:08:51,010 --> 00:08:56,010 we can save this as the selected_row. And then inside the selected_row, 134 00:08:58,080 --> 00:09:01,890 we can get to the tile at the horizontal position that was specified. 135 00:09:02,400 --> 00:09:07,400 So we could say selected row at the position of the horizontal - 1. 136 00:09:09,960 --> 00:09:14,910 This works the same way because our numbers that we're entering here, 137 00:09:14,910 --> 00:09:19,470 row one, two, three, or column one, two, three, they don't start from zero. 138 00:09:19,620 --> 00:09:23,730 So we have to shift it down by one in order for it to work. 139 00:09:24,300 --> 00:09:28,770 So, now once we've gotten hold of the selected row using the vertical, 140 00:09:29,280 --> 00:09:32,820 and then the selected tile using the horizontal, well, 141 00:09:32,820 --> 00:09:34,320 now we can actually change it. 142 00:09:34,710 --> 00:09:38,520 And the thing we want to change it to is a capital X. 143 00:09:39,210 --> 00:09:42,540 So now if I go ahead and run my code, 144 00:09:42,870 --> 00:09:47,370 then you can see it works just as the instructions want it to work. 145 00:09:47,760 --> 00:09:51,570 So here's our map. Where do you wanna put the treasure? If I write 146 00:09:51,570 --> 00:09:55,830 23, then it will put the treasure on column number two, row 147 00:09:55,860 --> 00:09:59,880 number three. Now, if I run this code again and I say, well, 148 00:09:59,880 --> 00:10:03,810 now I want to put it in column number one, row number three, 149 00:10:04,140 --> 00:10:05,190 then there it is. 150 00:10:05,520 --> 00:10:10,170 So this is now working for any possible combination that we come up with 151 00:10:10,380 --> 00:10:13,380 as long as we're using the coordinates of our map. 152 00:10:14,400 --> 00:10:18,630 Did you manage to get it right? And did you write the code in a different way, 153 00:10:18,630 --> 00:10:23,190 perhaps? Because there's many, many ways of doing the same thing. 154 00:10:23,760 --> 00:10:28,290 And the easiest thing that I can spot right now is what if we didn't need to 155 00:10:28,290 --> 00:10:33,290 separate this into two lines? Instead of creating a selected row, 156 00:10:33,960 --> 00:10:37,350 we could simply just tag on this at the end, 157 00:10:38,310 --> 00:10:41,400 get a hold of this particular row from the map, 158 00:10:41,700 --> 00:10:44,970 and because this is going to turn into a list, 159 00:10:46,020 --> 00:10:48,660 namely one of these, well, 160 00:10:48,660 --> 00:10:53,660 then we can simply just use another square bracket to specify the column. 161 00:10:55,200 --> 00:10:59,190 And then we set that tile to a capital X. 162 00:10:59,580 --> 00:11:03,450 So depending on which format you find it easier to understand, 163 00:11:03,730 --> 00:11:06,960 you can keep your code either like this or like this. 164 00:11:07,260 --> 00:11:09,060 This is obviously a lot more succinct, 165 00:11:09,120 --> 00:11:12,030 but it depends on whether if this logic actually makes sense to you. 166 00:11:12,840 --> 00:11:14,550 So have a think about what happened here, 167 00:11:14,790 --> 00:11:18,840 and if you didn't manage to complete the exercise, then try to give it another go. 168 00:11:18,840 --> 00:11:20,880 Now in the next lesson, 169 00:11:21,150 --> 00:11:24,780 we're going to tackle our final project of the day. 170 00:11:25,140 --> 00:11:28,680 So once you're prepared and once you're happy that you have understood 171 00:11:28,680 --> 00:11:30,840 everything that we've covered so far, 172 00:11:31,170 --> 00:11:34,920 then head over to the next lesson where we're going to get started building our 173 00:11:34,920 --> 00:11:36,510 rock-paper-scissors game. 16805