Binary Tree Postorder Traversal

Iterative Solution

Recursive 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 postorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
        if not root:
            return []
        
        res = []
        def r(node):
            if node.left:
                r(node.left)
            
            if node.right:
                r(node.right)
                
            res.append(node.val)
 
        
        r(root)
 
        return res

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References

https://leetcode.com/problems/binary-tree-postorder-traversal/