1 00:00:01,200 --> 00:00:02,670 All right, it's time for yet another 2 00:00:02,670 --> 00:00:04,410 difficult coding exercise. 3 00:00:04,410 --> 00:00:06,090 So this is a difficult challenge. 4 00:00:06,090 --> 00:00:08,340 What you're going to do is you're going to pretend 5 00:00:08,340 --> 00:00:09,750 to be a pirate. 6 00:00:09,750 --> 00:00:10,890 What do I mean by that? 7 00:00:10,890 --> 00:00:13,800 We're going to use what we've learned about lists 8 00:00:13,800 --> 00:00:15,750 and especially nested lists 9 00:00:15,750 --> 00:00:18,120 in order to create a Treasure Map. 10 00:00:18,120 --> 00:00:22,560 So we've created a Treasure Map by creating three lists 11 00:00:22,560 --> 00:00:25,860 which I've called line1, line2, and line3, 12 00:00:25,860 --> 00:00:29,130 and I've combined them into a nested list 13 00:00:29,130 --> 00:00:31,200 by using the code line four, 14 00:00:31,200 --> 00:00:33,240 where I said, map equals 15 00:00:33,240 --> 00:00:36,150 another list that contains three lists. 16 00:00:36,150 --> 00:00:40,860 Your job is to take an input in a similar format 17 00:00:40,860 --> 00:00:43,440 to how you see maps are formatted, 18 00:00:43,440 --> 00:00:46,410 where we can take a letter and a number 19 00:00:46,410 --> 00:00:48,750 and then use those letters and numbers 20 00:00:48,750 --> 00:00:52,290 to access a particular location in our list 21 00:00:52,290 --> 00:00:57,000 and convert the entry into an X 22 00:00:57,000 --> 00:01:01,230 to mark a spot on our map where we've buried our treasure. 23 00:01:01,230 --> 00:01:04,170 Have a read through the instructions carefully, 24 00:01:04,170 --> 00:01:06,930 figure out how this is supposed to work, 25 00:01:06,930 --> 00:01:09,630 and then write your code in main.py 26 00:01:09,630 --> 00:01:13,290 between the two sections that I've already written for you. 27 00:01:13,290 --> 00:01:14,850 So we've got a print statement 28 00:01:14,850 --> 00:01:16,920 that prints out all three lines, 29 00:01:16,920 --> 00:01:18,930 and you shouldn't change any of the existing code 30 00:01:18,930 --> 00:01:21,450 in order to complete this challenge. 31 00:01:21,450 --> 00:01:22,410 It's a difficult one. 32 00:01:22,410 --> 00:01:23,550 Have a think about it. 33 00:01:23,550 --> 00:01:26,310 Think about the Example Inputs and Example Outputs 34 00:01:26,310 --> 00:01:28,773 in the instructions and give this a go. 35 00:01:39,601 --> 00:01:40,600 All right. 36 00:01:40,600 --> 00:01:41,460 I did warn you it's a difficult one, 37 00:01:41,460 --> 00:01:43,860 but there's no shame in checking the solution, 38 00:01:43,860 --> 00:01:46,500 especially if you've given it a good go. 39 00:01:46,500 --> 00:01:48,750 The first thing that our code does 40 00:01:48,750 --> 00:01:53,750 is to grab hold of the first letter that's in the input. 41 00:01:53,820 --> 00:01:57,780 In this case, it is B in the example input. 42 00:01:57,780 --> 00:02:00,180 And what we're going to do is we're going to use position 43 00:02:00,180 --> 00:02:02,100 which takes the entire input, 44 00:02:02,100 --> 00:02:05,640 get the letter at the first index, 45 00:02:05,640 --> 00:02:08,490 so, position[0] 46 00:02:08,490 --> 00:02:12,093 and now we have that first letter from the input. 47 00:02:13,050 --> 00:02:14,400 Now the next thing we're going to do 48 00:02:14,400 --> 00:02:17,940 is we're going to turn this letter into lowercase 49 00:02:17,940 --> 00:02:21,570 so that we can compare it against a comparable. 50 00:02:21,570 --> 00:02:23,790 I've used the .lower() on line eight 51 00:02:23,790 --> 00:02:27,030 in order to lowercase the input letter 52 00:02:27,030 --> 00:02:29,430 just in case a user used the capital. 53 00:02:29,430 --> 00:02:32,580 And then on line nine, I've created a list 54 00:02:32,580 --> 00:02:34,950 that represents the three possible letters. 55 00:02:34,950 --> 00:02:36,600 We've got a, b, and c. 56 00:02:36,600 --> 00:02:39,358 Now, you could do it the other way 57 00:02:39,358 --> 00:02:40,860 and make it go uppercase as well, 58 00:02:40,860 --> 00:02:42,720 but everything has to be uniform 59 00:02:42,720 --> 00:02:46,020 in order to make sure that the user input 60 00:02:46,020 --> 00:02:48,600 doesn't matter if they put in lowercase or uppercase, 61 00:02:48,600 --> 00:02:51,480 our code will still work and can compare it 62 00:02:51,480 --> 00:02:54,633 against the values in this list of a, b, c. 63 00:02:55,560 --> 00:02:57,750 In order to do the comparison, 64 00:02:57,750 --> 00:03:01,560 we're using a method that comes from the Python list 65 00:03:01,560 --> 00:03:03,300 called index. 66 00:03:03,300 --> 00:03:05,010 So the way that we do this 67 00:03:05,010 --> 00:03:08,610 is we take the name of the list, which is a, b, c, 68 00:03:08,610 --> 00:03:10,710 and then we write .index, 69 00:03:10,710 --> 00:03:13,170 and then in the parentheses of that method, 70 00:03:13,170 --> 00:03:15,630 we pass in whatever it is we want to check 71 00:03:15,630 --> 00:03:17,760 that exists in the list. 72 00:03:17,760 --> 00:03:22,760 If the letter was b, as in this case in our input, 73 00:03:22,950 --> 00:03:27,630 then abc.index(b) is going to give us a number, 74 00:03:27,630 --> 00:03:29,280 it's going to give us 1, 75 00:03:29,280 --> 00:03:31,320 because remember lists start from 0. 76 00:03:31,320 --> 00:03:34,320 So a is at index 0, b is at 1, c is at 2. 77 00:03:34,320 --> 00:03:37,980 So now letter_index is 1, 78 00:03:37,980 --> 00:03:41,670 and we can work with it in order to get hold of the item 79 00:03:41,670 --> 00:03:44,400 in our map that we want to change. 80 00:03:44,400 --> 00:03:47,730 This part is a little bit difficult to conceptualize, 81 00:03:47,730 --> 00:03:50,460 but you can try thinking about this code, 82 00:03:50,460 --> 00:03:52,290 printing out what the values are 83 00:03:52,290 --> 00:03:54,450 and making sure you understand. 84 00:03:54,450 --> 00:03:57,690 The next part is getting hold of the number_index 85 00:03:57,690 --> 00:03:58,740 which is a lot easier 86 00:03:58,740 --> 00:04:01,260 because we can simply take the input 87 00:04:01,260 --> 00:04:03,960 which comes in through the variable position, 88 00:04:03,960 --> 00:04:05,670 get the value at index 1 89 00:04:05,670 --> 00:04:10,590 which is the second digit or letter in the input, 90 00:04:10,590 --> 00:04:12,990 and in this case, it's the number 3. 91 00:04:12,990 --> 00:04:14,460 And in our map 92 00:04:14,460 --> 00:04:18,660 because we have a list and remember lists start from 0, 93 00:04:18,660 --> 00:04:22,770 s o actually position 3 is equivalent to index 2. 94 00:04:22,770 --> 00:04:27,210 So we always have to subtract 1 in order to get the index 95 00:04:27,210 --> 00:04:30,270 because it starts counting from 0. 96 00:04:30,270 --> 00:04:32,613 So now we have the number_index. 97 00:04:33,570 --> 00:04:37,770 Finally, we can bring up our nested list, our map, 98 00:04:37,770 --> 00:04:40,740 and put in both of these indices 99 00:04:40,740 --> 00:04:44,550 in order to change the item at that position 100 00:04:44,550 --> 00:04:46,410 to the letter X. 101 00:04:46,410 --> 00:04:49,170 The thing that might be a little bit confusing here 102 00:04:49,170 --> 00:04:53,610 is the first part is actually the number_index 103 00:04:53,610 --> 00:04:57,150 because remember we said that with nested lists 104 00:04:57,150 --> 00:05:00,090 we go from outside to in. 105 00:05:00,090 --> 00:05:03,660 And what that means is we've got a list of lists. 106 00:05:03,660 --> 00:05:08,660 So if you look at line four, our outer list is our map 107 00:05:09,270 --> 00:05:11,910 with line1, line2, line3, 108 00:05:11,910 --> 00:05:15,510 and the part of our input that determines 109 00:05:15,510 --> 00:05:18,060 which of those lines we're going to pick out 110 00:05:18,060 --> 00:05:20,670 is actually the number, not the letter. 111 00:05:20,670 --> 00:05:23,400 So that's why the first index that goes in 112 00:05:23,400 --> 00:05:24,990 is the number_index. 113 00:05:24,990 --> 00:05:27,540 And then once we've gotten onto the correct 114 00:05:27,540 --> 00:05:29,730 line1, line2, or line3, 115 00:05:29,730 --> 00:05:31,290 then we use the letter_index 116 00:05:31,290 --> 00:05:33,210 in order to pick out the right element 117 00:05:33,210 --> 00:05:36,840 in that nested inner list. 118 00:05:36,840 --> 00:05:38,940 This again, is a little bit mind blowing. 119 00:05:38,940 --> 00:05:41,310 It's difficult to get your head around, 120 00:05:41,310 --> 00:05:44,070 but it's okay if you just try it a few times, 121 00:05:44,070 --> 00:05:47,040 try the code, try some different combinations 122 00:05:47,040 --> 00:05:49,200 and eventually you will get around 123 00:05:49,200 --> 00:05:51,300 to this programmer's way of thinking 124 00:05:51,300 --> 00:05:52,890 which is a little bit different 125 00:05:52,890 --> 00:05:54,660 to what you might be used to. 126 00:05:54,660 --> 00:05:56,010 Be patient with yourself. 127 00:05:56,010 --> 00:05:57,600 If you have any changes you need to make, 128 00:05:57,600 --> 00:05:59,900 go back to the previous slide and make it now.