1 00:00:00,720 --> 00:00:03,150 Hi everyone, let's do this question. 2 00:00:03,150 --> 00:00:09,420 You are given two non-empty linked lists representing two non-negative integers. 3 00:00:09,420 --> 00:00:15,780 The digits are stored in reverse order, and each of their nodes contains a single digit. 4 00:00:15,780 --> 00:00:19,440 Add the two numbers and return the sum as a linked list. 5 00:00:19,440 --> 00:00:21,690 So that's the question and why it's mentioned. 6 00:00:21,690 --> 00:00:29,040 You may assume the two numbers do not contain any leading zero except the number zero itself, and then 7 00:00:29,040 --> 00:00:31,440 the value of a node is between 0 and 9. 8 00:00:31,440 --> 00:00:31,890 All right. 9 00:00:31,890 --> 00:00:33,720 So again that's mentioned over here as well. 10 00:00:33,720 --> 00:00:36,150 So it's a single digit the value if every node. 11 00:00:36,180 --> 00:00:42,720 Now the question says that we are given two non-empty linked lists and they are non-negative integers. 12 00:00:42,720 --> 00:00:46,440 And then the value is stored in reverse order. 13 00:00:46,440 --> 00:00:48,270 So again let's try to understand that. 14 00:00:48,270 --> 00:00:52,710 So for example if the numbers that we want to add because we have to add them right. 15 00:00:52,710 --> 00:01:01,800 So if the numbers that we want to add add are 123 and let's say 751 now because the digits are stored 16 00:01:01,800 --> 00:01:04,920 in reverse order, the linked list will look like this. 17 00:01:04,920 --> 00:01:07,440 We'll have three going to two going to one. 18 00:01:07,440 --> 00:01:12,720 So that's the reverse order right from three to 2 to 1 and then one to 5 to 7. 19 00:01:12,720 --> 00:01:14,460 So that's the reverse order. 20 00:01:14,460 --> 00:01:16,050 That is what is mentioned over here. 21 00:01:16,050 --> 00:01:21,090 Now we need to add these up together and then return the sum as a linked list. 22 00:01:21,090 --> 00:01:25,860 So for example over here if we add these two we will get 874 right. 23 00:01:25,860 --> 00:01:29,880 So we have to return this which is the sum as a linked list. 24 00:01:29,880 --> 00:01:32,340 So again that should be in the reverse order. 25 00:01:32,340 --> 00:01:34,290 So we will have four going to seven. 26 00:01:34,290 --> 00:01:35,820 And then that's going to eight. 27 00:01:35,820 --> 00:01:37,440 So that is this order over here. 28 00:01:37,950 --> 00:01:39,210 So that's the question over here. 29 00:01:39,210 --> 00:01:44,220 And then it's mentioned that you may assume the two numbers do not contain any leading zero. 30 00:01:44,220 --> 00:01:47,340 So there won't be a case like 074. 31 00:01:47,340 --> 00:01:53,340 Like for 74 it would be just 74 not 074, except the number zero itself. 32 00:01:53,340 --> 00:01:57,630 So that this is a possibility 000 because that's just the number zero. 33 00:01:57,630 --> 00:01:58,950 Now this is the question. 34 00:01:58,950 --> 00:02:00,600 Now it's pretty straightforward. 35 00:02:00,600 --> 00:02:06,330 Now let's go ahead and look at a few test cases for this so that we get a good understanding of this 36 00:02:06,330 --> 00:02:06,960 question. 37 00:02:07,410 --> 00:02:12,000 Now let's say we want to add 540 and 723. 38 00:02:12,000 --> 00:02:16,050 Now when we add them we will get 1263. 39 00:02:16,050 --> 00:02:20,040 So this has to be returned as a linked list in the reverse order. 40 00:02:20,040 --> 00:02:23,130 So we have three going to six going to two going to one. 41 00:02:23,130 --> 00:02:28,110 Now the interesting thing to notice over here is there is nothing over here in these two linked lists. 42 00:02:28,110 --> 00:02:30,810 But in the output we have four nodes. 43 00:02:30,810 --> 00:02:32,640 That's something interesting to note. 44 00:02:32,640 --> 00:02:35,640 Now what if we want to add 99 and 16. 45 00:02:35,640 --> 00:02:37,530 Again it's going to be in the reverse order. 46 00:02:37,530 --> 00:02:40,530 So we have nine going to nine and then six going to one. 47 00:02:40,530 --> 00:02:43,170 And when we add them we will get 115. 48 00:02:43,170 --> 00:02:45,540 So the output also is in the reverse order. 49 00:02:45,540 --> 00:02:47,820 So five goes to one and that goes to one. 50 00:02:47,820 --> 00:02:49,950 So this is the output linked list. 51 00:02:49,980 --> 00:02:53,250 Now what if we want to add 729 and 53. 52 00:02:53,250 --> 00:02:57,750 Now you can see the length of the two linked lists need not be the same. 53 00:02:57,750 --> 00:02:58,950 Again we can add them. 54 00:02:58,950 --> 00:03:00,570 We will get 782. 55 00:03:00,570 --> 00:03:02,070 And that would be the output. 56 00:03:02,070 --> 00:03:04,350 So two goes to eight and that goes to seven. 57 00:03:04,350 --> 00:03:05,700 So that's the reverse order. 58 00:03:05,700 --> 00:03:09,120 And then let's say one linked list is null. 59 00:03:09,120 --> 00:03:10,650 So there is nothing over here. 60 00:03:10,650 --> 00:03:12,810 And then we have zero going to one. 61 00:03:12,810 --> 00:03:14,040 So that's actually ten right. 62 00:03:14,040 --> 00:03:15,270 So ten plus nothing. 63 00:03:15,270 --> 00:03:16,950 So that gives us ten itself. 64 00:03:17,040 --> 00:03:18,720 So that is also a possibility. 65 00:03:18,720 --> 00:03:21,540 So one of the linked lists could just be null or empty. 66 00:03:21,540 --> 00:03:23,430 So we have understood the question. 67 00:03:23,430 --> 00:03:26,910 And we have looked at a few test cases together. 68 00:03:26,910 --> 00:03:28,110 In the next video. 69 00:03:28,110 --> 00:03:30,960 Let's try to think how we can solve this question.