[Solved] Given the root of a binary tree, return the zigzag level order traversal of its nodes’ values. (i.e., from left to right, then right to left for the next level and alternate between).

Question

Given the root of a binary tree, return the zigzag level order traversal of its nodes’ values. (i.e., from left to right, then right to left for the next level and alternate between).

Example 1:

Machine Learning Projects
Input: root = [3,9,20,null,null,15,7]
Output: [[3],[20,9],[15,7]]

Example 2:

Input: root = [1]
Output: [[1]]

Example 3:

Input: root = []
Output: []

Constraints:

  • The number of nodes in the tree is in the range [0, 2000].
  • -100 <= Node.val <= 100

Python Solution

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def zigzagLevelOrder(self, root: TreeNode) -> List[List[int]]:
        if root==None:return None
        res = []
        q = [root]
        level = 1
        
        while q:
            tempq = []
            lev = []
            while q:
                curr = q.pop(0)
                lev.append(curr.val)
                if curr.left :tempq.append(curr.left)
                if curr.right :tempq.append(curr.right)
            q = tempq
            if not level%2:
                res.append(reversed(lev))
            else:
                res.append(lev)
            level+=1
        return res
Abhishek Sharma
Abhishek Sharma

Started my Data Science journey in my 2nd year of college and since then continuously into it because of the magical powers of ML and continuously doing projects in almost every domain of AI like ML, DL, CV, NLP.

Articles: 514

Leave a Reply

Your email address will not be published. Required fields are marked *