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# Postorder Traversal

Problem Description

Given a binary tree, return the Postorder traversal of its nodes values.

NOTE: Using recursion is not allowed.

Problem Constraints

1 <= number of nodes <= 105

Input Format

First and only argument is root node of the binary tree, A.

Output Format

Return an integer array denoting the Postorder traversal of the given binary tree.

Example Input

Input 1:

```   1
\
2
/
3```

Input 2:

```   1
/ \
6   2
/
3```

Example Output

Output 1:

` [3, 2, 1]`

Output 2:

` [6, 3, 2, 1]`

Example Explanation

Explanation 1:

` The Preoder Traversal of the given tree is [3, 2, 1].`

Explanation 2:

` The Preoder Traversal of the given tree is [6, 3, 2, 1].`

NOTE: You only need to implement the given function. Do not read input, instead use the arguments to the function. Do not print the output, instead return values as specified. Still have a question? Checkout Sample Codes for more details.
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