Binary Tree Zigzag Level Order Traversal - LeetCode 103 Python

Explaining Binary Tree Zigzag Level Order Traversal in Python

Music: Bensound

Lemme know up if y'all have any questions/comments!:)

[abhineetsharma]

Great vid ! Your explanation was very idiosyncratic and conspicuous.


Just a quick question tho, how do I get to your level ? Your approach to the problem made it seem so easy.
But whenever I look at these sorta questions I sit completely blank with Zilch in my mind.

I have solved approximately 100 questions on LeetCode so far on different topics but still I just can't come up
with a solution right away.


Is there something that you can suggest for a better way of solving problems like these other than brute force ?

[pathapac]

Great explanation there Deepti. This is the first video I am watching from you and already a fan. Keep going and please help with any useful links/online content which can help me get better to think through any Algo-DS related questions

[HariHaran-slpg]

Can anyone explain me how this is O(n)..there were two while loops inside a while loop..plz explain

[sagarpotnis]

really good solution! thank you so much

[hildesong]

Thank you very much for the walk throught!!

[Mohib]

so when you pop. the type of root should be TreeNode right. But leetcode is saying it is of Type Int

root = s1.pop()
level.append(root.val) ---> Getting error for this saying type int has no attribute val

[shubhamkurup]

It's so well explained especially in the last 2 mins. Thank you.

[AnshuKumar-znqb]

Well explained Plz upload more videos ...🙏🏿

[anmolwadali]

good !! plz make videos on strings questions

[anasshah]

Very nice effort. what i think that you can perform this in such a way that apply dfs, if its even level go from left to right and if its even move from right to left. In this way you can optimise your solution.

[aaditkamat]

Good explanation, Deepti. I'm using your videos in tandem with those by Neetcode to brush up on my DS and Algos. I like how you walkthrough the problems using the Leetcode interface. At the moment, I keep tripping up by making silly mistakes with the references or missing out some things even if I know the algorithm.

[Kushagra_]

plzz help with the iterative postorder a bit more complex than other 2 traversls....please help with this.

[saibharadwajvedula]

This is so cool! but why are we checking if level != []

[parvathirajan.n]

A small trick with Level Order traversal would also work.

class Solution:
def zigzagLevelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
if not root:
return []

queue = [root]
level = []
result = []
lvl = 0

while queue:
q2 = []
for root in queue:
level.append(root.val)
if root.left:
q2.append(root.left)
if root.right:
q2.append(root.right)

result.append(level if lvl % 2 == 0 else reversed(level))
level = []
queue = q2
lvl += 1

return result