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#145. Binary Tree Postorder Traversal | LeetCode Python Solution

Problem​

LeetCode Problem

  1. Binary Tree Postorder Traversal

Python Solution with Recursion​

# 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:
    # Postorder (Left, Right, Root)
    def postorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
        # Handle base cases
        if root is None:
            return []
        elif root.left is None and root.right is None:
            return [root.val]

        # Output list
        output = []

        # Collect left subtree values
        if root.left is not None:
            output = self.postorderTraversal(root.left)

        # Collect right subtree values
        if root.right is not None:
            output.extend(self.postorderTraversal(root.right))

        # Collect root node value
        output.append(root.val)

        return output