1 00:00:00,770 --> 00:00:01,700 Hi everyone. 2 00:00:01,700 --> 00:00:03,590 Let's do this question now. 3 00:00:03,590 --> 00:00:06,710 This question is about designing a singly linked list. 4 00:00:06,710 --> 00:00:07,790 So let's read it. 5 00:00:07,790 --> 00:00:12,020 Design a singly linked list class that has a head and tail. 6 00:00:12,020 --> 00:00:18,230 Every node is to have two attributes value the value of the current node, and next a pointer to the 7 00:00:18,230 --> 00:00:18,950 next node. 8 00:00:18,950 --> 00:00:21,050 The linked list is to be zero indexed. 9 00:00:21,050 --> 00:00:22,970 The class should support the following. 10 00:00:22,970 --> 00:00:23,960 So that's the question. 11 00:00:23,960 --> 00:00:25,700 Now the class should support the following. 12 00:00:25,700 --> 00:00:28,220 The first is we have singly linked list over here. 13 00:00:28,220 --> 00:00:31,100 Now this initializes the singly linked list object. 14 00:00:31,100 --> 00:00:35,420 So we have seen previously that a class is a blueprint for creating objects. 15 00:00:35,420 --> 00:00:37,070 So it's defining a pattern. 16 00:00:37,070 --> 00:00:40,880 And objects can have uh parameters and methods. 17 00:00:40,880 --> 00:00:42,110 So we have seen that before. 18 00:00:42,110 --> 00:00:42,470 All right. 19 00:00:42,470 --> 00:00:46,670 So again we will just have a class and its name will be singly linked list. 20 00:00:46,670 --> 00:00:52,550 And then we can just say uh const um singly linked list one is equal to new singly linked list. 21 00:00:52,550 --> 00:00:55,100 So that's how we will create this object over here. 22 00:00:55,100 --> 00:00:55,460 All right. 23 00:00:55,460 --> 00:00:57,530 So this is going to be pretty straightforward. 24 00:00:57,530 --> 00:00:58,790 And we have seen this before. 25 00:00:58,790 --> 00:01:01,910 And we will again visit this when we code out our solution. 26 00:01:01,910 --> 00:01:04,010 Now let's read the remaining part over here. 27 00:01:04,010 --> 00:01:08,240 It's mentioned that some instance methods should be written for this particular class. 28 00:01:08,240 --> 00:01:11,450 So the first instance method is get index. 29 00:01:11,450 --> 00:01:13,610 Now over here the index is passed to it. 30 00:01:13,610 --> 00:01:16,670 Now this should get the value of the index node. 31 00:01:16,670 --> 00:01:19,250 If the index is invalid return minus one. 32 00:01:19,250 --> 00:01:22,070 So for example if our singly linked list is something like this. 33 00:01:22,070 --> 00:01:24,020 So we have one pointing to two. 34 00:01:24,020 --> 00:01:26,630 And then we have this pointing to a node with value three. 35 00:01:26,630 --> 00:01:27,860 And this points to null. 36 00:01:27,860 --> 00:01:29,240 So this is a singly linked list. 37 00:01:29,240 --> 00:01:33,830 Now if we pass index one then it should get this particular node over here. 38 00:01:33,830 --> 00:01:38,030 Again this is index zero because it's mentioned that the linked list is to be zero indexed. 39 00:01:38,030 --> 00:01:38,840 So this is zero. 40 00:01:38,840 --> 00:01:40,220 This is one and this is two. 41 00:01:40,220 --> 00:01:45,980 And again remember we cannot do this in constant time as in the case of an array because the indices 42 00:01:45,980 --> 00:01:48,980 are not stored um in inbuilt manner. 43 00:01:48,980 --> 00:01:49,220 Right. 44 00:01:49,220 --> 00:01:52,610 So we'll have to traverse and we'll have to use a count variable for that. 45 00:01:52,610 --> 00:01:52,970 All right. 46 00:01:53,000 --> 00:01:54,710 Now let's continue reading the question. 47 00:01:54,710 --> 00:01:59,480 The next instance method is add add head and a value is passed to it. 48 00:01:59,870 --> 00:02:01,310 So a value would be passed. 49 00:02:01,310 --> 00:02:05,690 And we have to add a node of the given value before the first element of the linked list. 50 00:02:05,690 --> 00:02:11,060 So for example, if the value four is passed and added head instance method is called for this singly 51 00:02:11,060 --> 00:02:15,920 linked list, then we would have to make a node with value four and that should be added at the head. 52 00:02:16,400 --> 00:02:18,590 So that's the second instance method over here. 53 00:02:18,590 --> 00:02:21,470 Now the next one is add a tail and a value is passed. 54 00:02:21,470 --> 00:02:24,350 So again in a similar manner if we want to add five. 55 00:02:24,350 --> 00:02:25,790 So we would have to add it over here. 56 00:02:25,790 --> 00:02:29,150 So this three will be pointing to five which will point to null. 57 00:02:29,150 --> 00:02:33,410 So add a node of given value at the last element of the linked list. 58 00:02:33,440 --> 00:02:40,130 Now the next instance method is added index and index and value is passed to add a node of given value 59 00:02:40,130 --> 00:02:43,250 before the index node in the linked list. 60 00:02:43,250 --> 00:02:48,500 If the index equals the length of the linked list, the node will be appended to the end of the linked 61 00:02:48,500 --> 00:02:48,800 list. 62 00:02:48,800 --> 00:02:52,190 If index is greater than the length, don't insert the node. 63 00:02:52,190 --> 00:02:53,720 So this is very clear. 64 00:02:53,720 --> 00:02:58,910 So for example in this linked list over here let's write the indices zero, one two and three. 65 00:02:58,910 --> 00:03:04,640 So if the index is equal to four over here when we call this function then we will add it at the end 66 00:03:04,640 --> 00:03:05,240 as the tail. 67 00:03:05,240 --> 00:03:07,700 So it's mentioned over here if index equals the length. 68 00:03:07,700 --> 00:03:09,230 So the length over here is four. 69 00:03:09,230 --> 00:03:11,840 The node will be appended to the end of the linked list. 70 00:03:11,840 --> 00:03:14,900 If index is greater than the length for example over here the length is four. 71 00:03:14,900 --> 00:03:17,360 And index let's say is 5 or 10. 72 00:03:17,360 --> 00:03:19,220 In that case we won't insert the node. 73 00:03:19,220 --> 00:03:20,600 So that's what is mentioned over here. 74 00:03:20,600 --> 00:03:25,610 And then if we want to insert a node at index one, it's going to be inserted before this. 75 00:03:25,610 --> 00:03:29,000 So that the new node let's say that's value that has value five. 76 00:03:29,000 --> 00:03:29,750 The new node. 77 00:03:29,750 --> 00:03:33,470 Once it is inserted over here it will be at index one. 78 00:03:33,800 --> 00:03:35,180 So that is what is mentioned over here. 79 00:03:35,180 --> 00:03:39,410 Add a node of given value before the index node in the linked list. 80 00:03:39,410 --> 00:03:42,440 So that is added index function or method over here. 81 00:03:42,440 --> 00:03:45,830 And then the last instance method is delete at index. 82 00:03:45,830 --> 00:03:47,570 And we only pass the index. 83 00:03:47,570 --> 00:03:51,590 So delete the index node in the linked list if the index is valid. 84 00:03:51,590 --> 00:03:52,820 Else nothing happens. 85 00:03:52,820 --> 00:03:58,700 So for example, if this is the linked list and we want to delete this particular node, then this will 86 00:03:58,700 --> 00:03:59,150 be removed. 87 00:03:59,150 --> 00:04:00,800 And this will point to the next node. 88 00:04:00,800 --> 00:04:03,260 So these are the instance methods that we have to write. 89 00:04:03,260 --> 00:04:07,550 So let's go ahead and see in the next video how we can solve this question.