Postorder Traversal (Iterative)
Medium Accuracy: 77.23% Submissions: 6509 Points: 4

Given a binary tree. Find the postorder traversal of the tree without using recursion.

Example 1

Input:
           1
         /   \
        2     3
      /  \
     4    5

Output: 4 5 2 3 1
Explanation:
Postorder traversal (Left->Right->Root) of 
the tree is 4 5 2 3 1.

Example 2

Input:
             8
          /      \
        1          5
         \       /   \
          7     10    6
           \   /
            10 6

Output: 10 7 1 6 10 6 5 8 
Explanation:
Inorder traversal (Left->Right->Root) 
of the tree is 10 7 1 6 10 6 5 8 .
 
Your task:
You don't need to read input or print anything. Your task is to complete the function postOrder() which takes the root of the tree as input and returns a list containing the postorder traversal of the tree, calculated without using recursion.
 
Expected time complexity: O(N)
Expected auxiliary space: O(N)
 
Constraints:
1 <= Number of nodes <= 105
1 <= Data of a node <= 105

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Postorder Traversal (Iterative)

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