Binary Tree Level Order Traversal

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This question is commonly asked by the following companies: Google, Facebook, Amazon, Uber, Microsoft, Oracle, Bloomberg, LinkedIn, and Walmart Labs.

Intuition behind solution: Create a queue and add the root to the queue. While the queue is not empty process all the nodes in the queue. At every iteration of the queue not being empty, get the size of the queue (this represents however many nodes are on the current level of the tree). Iterate through all these nodes with a for loop, adding their values to a "current level" list. After adding their value to the list, check if they have left and right children adding them to the queue is they do exist (this allows us to process the next level of the tree on the next iteration of our while loop). Once our for loop terminates we have populated a list of all the nodes' values on the current level and we add this list to our return value (a list of lists). Once our while loop ends we have processed all the levels of the true and therefore return our result (our list of lists).

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Blushes by Dj Quads
rose & boujee by memori ("me over mori")

[jeremyvan]

came for the BFS advice, stayed for the chill lofi migos remix

[dephcn]

I am glad I saw your link in the leetcode discussion. I need to practice more queue and stack "iterative recursive" algorithms.

[readonlylogin]

Such a simple and genius explanation! Before this video BFS for me was harder than recursive DFS. Now I can understand both. Big thanks to you!

[soniagrzywocz]

This is amazing. I struggled understanding BFS but this is the best explanation I have seen so far. Thank you so much!

[alankardingshsingh]

Very helpful video, I was struggling with the explanation on leetcode. This video made it too easier to understand and that too in minimum amount of time. Thank you!

[zaidaldhahi]

You're very awesome. I always search for your videos first whenever I get stuck in a leetcode problem. Thanks a lot

[shubhammittalSHM]

That Walmart Labs gesture was hilarious though! Please upload some videos for Linked Lists as well.

[stanleerubio]

always coming thru w a clear and concise explanation/approach.good looks bro keep it up!

[RomanReigns-tgqm]

Awesome man! BFS within just 5 minutes with such clear explanation

[xxpirategamingxx]

Thank you, very much, i was stuck since it was hard to keep track of levels

[punerealestatebuilder]

The "int size = queue.size()" was the trick and I was missing it :). Great

[jamesvick]

My man has exquisite music taste. I love it lol

[SreeOne]

Have been looking for the level-specific control over the BFS for a while. The trick found in this video is to iterate the level with the queue length.
This trick is also useful to find the level-average of a tree (another FB question on Leet) Thanks man!!! also watched the running gurlfriend behind you in other videos :-) lol..

[Spider-Man_]

Wow...so simple & superb explanation.

[TheSantouryou]

Short, easy, precise explanation. Thanks.

[maheshdudhanale]

@Kevin Naughton Jr.
Before watching your video, I implemented a level-order traversal that was okay, but it put everything in just one list.
But after watching your video I realised that I don't have to use just one dequeue operation for each enqueue operation.
Like a lightning that struck me.
And for size of current level, I was using 2^n kind of logic. but your answer simplified it very much.
Thank you very much!!!

[HarpreetSingh-eskq]

You are right. I always found it difficult to understand BFS and wound never forget it now. Thanks

[mythilikarra]

Yoo I am so thankful for your channel, I am able to learn a lot thanks to your easy explanations! Thank you so much!!

[darshansimha]

Man! I love your videos. Super cool explanation. I would love it if the background music was a bit less loud if that is okay by you!

[cakec]

Thank you thank you thank you. Such a simple and elegant solution!