LeetCode Add Two Numbers Solution Explained - Java
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- เผยแพร่เมื่อ 1 ต.ค. 2024
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Great.. one suggestion though. Please move your picture position to down left.
Already done in his newer videos, plus background is transparent.
You do not even try to have a different solution other than the posted solution in LeetCode for the question.
Its line by line same; even structure is same. What differs here is just name of the variables .. lol
I am noticing this for a lot of questions from you and believe me sometime you do not even try to explain why something is done in a tricky situation. Just the rote solution from leetcode.
Please come up with different solutions other than what leetcode already provides.
I am pretty sure in an interview setup typing almost the same solution as leetcode/algoExpert etc will cause issues as interviewers know and practice that question by looking at those solutions.
I am not here to judge you my friend but to suggest you that even if you refer those posted solution, when you code, go with your own coding flow and style. Do not come up with memorized posted solutions.
this solution is like the absolute best case scenario lol. It takes like a few minutes alone to even understand the scope of the output here. I completed a solution (100 lines of code LOL), but even after all that i forgot what if the sum of the last digits need a carry. I strongly doubt anyone aside from a CS prof or someone who deals with highly logical work (number theorist/mathematicians/Data scientists etc) can pull this off as fast as Nick did lol. Taking Data right now and this problem is equivalent to a weekly practice problem. A whole week. Took me 2 days to finish this particularly one...no where near 6 min.
Lol wish could of taken a hint from this but my prof doubles down on weekly programs and she would cut 3/4 points off if its not your logic.
Just try to learn and move on lol! Thank him at the very least. He helped a lot of people here
the numbers are bit confusing here because 243+564 = 807 and if you reverse the numbers 342+465 = 807
You do the addition backwards, instead of going right to left, go left to right when adding.
true, first time i looked at that example i thought i missed something
i get almost all of it, i can see how its added and carried over, i just dont understand which part revereses the linked node so that it can be added the way it is added
ListNode dummy_head = new ListNode(0);
what does the (0) mean, why we have it there?
It has a value of 0, its basically a neat trick you can do so you won't get a pointer error.
I dont get it. When we never assigned any next Node to dummy_head. How did dummy_head still print the right answer?
I do not get that as well. I was going to ask the same thing.
because all this time, l3 is modifying for dummy_head. When we point l3 to dummy_head and modify l3, we are also modifying dummy_head. Since we need l3 as a pointer to move around, we need dummy_head to stay at the head of the node to be returned.
Hey Nick, Thanks for the explanation. It would be a great help if you provide the solution of problem 445 i.e Add two numbers II.
hey. thanks for the video. Would be great if you could either decrease the sound of the keyboard clicks or use a better microphone.
BM BM just started using a better mic
Passes 1560/1563 test cases.
class Solution {
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
StringBuilder s1 = new StringBuilder("");
StringBuilder s2 = new StringBuilder("");
while(l1!=null){
s1.append(l1.val);
l1 = l1.next;
}
while(l2!=null){
s2.append(l2.val);
l2 = l2.next;
}
String t1 = s1.reverse().toString();
String t2 = s2.reverse().toString();
long i1 = Long.parseLong(t1);
long i2 = Long.parseLong(t2);
long i3 = i1+i2;
if(i3==0){
return new ListNode(0);
}
ListNode dummy = new ListNode(-1);
ListNode head = dummy;
while(i3!=0){
int k = (int)(i3%10);
i3 = i3/10;
head.next = new ListNode(k);
head = head.next;
}
return dummy.next;
}
}
Some how this was the only video that could explain the solution to me. thanks
thanks for sharing. very clear explanation. Im preparing for my interview, I like your video
is that capital one's hack t-shirt ur wearing?
good eye! Yeah it is
do we need line 36?
Line 36 not needed?
Yes, the answer would be accepted without the line 36 too.
this solution doesn't work when the digital number is different, 999+1 and 999+100 are different result, you should reverse the list first
yes it does work. the nodes are. 9->9->9->null and 0->0->1->null for 999+100 and 9->9->9->null and 1->null for 999+1. tested it. the results are 9->9->0->1->null and 0->0->0->1->null, respectively.
Imo it’s more convenient (val_1 + val_2) % 10 further we can check if val_1 + val2 >= 10
dang, you must've gotten a really good server since I keep getting "time limit exceeded" error. My code is very similar, I guess I got unlucky with the server being slow or something.
how is the carry not being brought over from the first time? wouldn’t it be .7?
Thank you brother for your explanation.
wat about the 0 in the list during initialization wouldnt that lead to a wrong answer?
Why?
What if we have much larger numbers? Sum must be long type right
Hello, Thanks to sharing ur specious knowledge.
But i got a error like "Time limit Exceeded".
Please help me for the same.
me too have you got any solution?
@@skm9865 you have skipped the increment part i.e. incrementing l1, l2 , l3 check that
@@aryaabhishek9535 I will check , thank you
@@aryaabhishek9535 I still get the time limit exceed. I have the code verbatim :(
He copies the solution code acting like he came up with it 😂.
Really easy tutorial to follow, thanks a ton!
This problem was so annoying
can someone explain why the l3 = dummy_head?
Thank u so much, Nick! it's very helpful. I finished mine in 1ms but my solution based on yours.^^
bro thanks for the content
Do you practice all problem beforehand and them present them here or is it you solve on the spot ??
He knows the answer already
obviously
Did this using stacks? Not sure if it’s calid
Please solve by ur own solution nick 😂
whats written on line number 34 after listNode new_node = new ?
ListNode new_node = new ListNode(carry);
Halo Nick..where is the Java Souce GitHub URL for each problem?Please share
What u worte in line 34 ?..not clear
Thank you! This was the first time I was able to understand the solution to this problem.
I like how dead his voice is.
You could improve this further by doing it with O(1) space if you reuse nodes of the longer number
It is not guaranteed if there even exists a longer node, say 99 + 99 = 198, and generally, changing the given parameters (ListNode* l1, ListNode* l2) is not the best practice.
this wont work when their is carry over
@@CD-xd6fm carryover is at most how many nodes? It's constant space.
@@AlbertoRodriguez-oe6jo if you're trying to optimize for space then it's OK. Yes, in real life it's not the best practice to modify objects from the arguments. Also what I meant is either the longer one or just a random one of the two..
@@coolilshat carry over is just one node.....but you were saying to overwrite the longer linked list...but let's say for e.g. 987+98 = 1085.....in this case you will need four nodes to store the answer but you are only having three
I'm confused why we need all the null checks. Because we are doing l1 != null OR l2 != null in the while loop, if either of these 2 values are null wouldn't it break out of the loop and not execute so we know they would never be null ?
This confused me too for a while. It's simple but a lot is going on so it is hard to understand right away. The while condition in English says: While *either* list is not null keep going. You are mistaking that for saying if either of the two list is null end the loop.
Anyway this means that either:
Both are null: The loop is done, print out our answer
Both are not null: Easy, we just keep going
One is null the other list has another number left : This is a bit trickier. i.e adding a list with 123 and the second list has = 1234, 123 would be null after 3, 1234 has "4" left. Thus list 1 is null list 2 still has another digit to go so the loop iterates one more time. After adding 4, both list are null we are done.
Now what does the second null check do? As I stated in case 3 one can be null but the other not null. We can not add 123NULL and 1234NULL because they don't line up. So we must replace null with a 0 (as we would writing math with a paper and pencil in real life) to "line it up" so to say.
*Reminder that the end of a list aka the tail is always null this is just a convention used so we know where to stop. *
@@kakashi99908 Thank you for your explanation!! Was having the same doubt
Nick offer(), and size() method what to do.please help me
what happened on 4:05??
Thanks
please move you Pic at left Bottom corner
I thought the same way. Thank you. You are awesome.
coding made easy
If in case of different size of list how it
Thank you for all your videos! verry helpfull
at first line of our code we are creating a null node right??
it's just a dummy node with a dummy value 0
Hi, I am just wondering that if the inputs params not linklist, they are 2 arrays, but one of them has longer length. how would you do this addition
is there a leetcode problem you can link? I'll just make a video if you can find one
@@NickWhite Hi Nick, this is just random question pop up in my head, I do not see one so far. For example, [1,2,3], [1,2,3,4]. if 2 array has same length it will be easy to do so. but if one of them has different length this will be interesting
@Patrick K That is a good way, Thanks.
@@lingsike3193 AFAIK arrays have fixed size in java and c++. You can't just add an element to it. Better would be to convert both arrays into a two numbers, add them, turn the answer to an array and return it.
You can convert array to num using:
int count = 1;
for(int i=0; i
Thank you sir.
whats written on line number 34 after listNode new_node = new ?
cool
Thank you
thanks!
Hi Nick, I'm using your videos to compare my solutions on many problems. It helped me a lot. Thaks a lot. Your always comes up with a new and greater solution.
dude could you please do solutions of codechef monthly challanges
what if the numbers are in non reversed order?. We should reverse both list and do this approach ?
write a reverse function pass list to it and then its all same
Thanks, man.
whats written on line number 34 after listNode new_node = new ?
@@raktimranjandeka2793 new ListNode ( carry)
cant understand the accent....smh
rahul raj my bad dude it’s just English but I can try and annunciate better
too bad he aint doing that hinde accent huh
XD lmao