103. Binary Tree Zigzag Level Order Traversal

103. Binary Tree Zigzag Level Order Traversal

# 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: Optional[TreeNode]) -> List[List[int]]:
        
        if not root:
            return []
        
        q = deque([root])
        ans = []
        count = 0
        
        
        while q:
            size = len(q)
            curr = []
            for _ in range(size):
                node = q.popleft()
                curr.append(node.val)
                if node.left:
                    q.append(node.left)
                if node.right:
                    q.append(node.right)
            if count%2 == 1:
                curr = curr[::-1]
            
            count += 1
            ans.append(curr)
        
        return ans