Find n-th node in postorder traversal of a binary Tree

In a postorder traversal of a binary tree, we visit the left subtree, then the right subtree, and finally the root node.

To find the n-th node in postorder traversal of a binary tree, we need to traverse the tree in postorder and count the nodes as we visit them. Once we have visited n nodes, we can return the value of the node we are currently at as the n-th node.

Here's a step-by-step approach to find the n-th node in postorder traversal:

1. Traverse the left subtree recursively, counting the nodes as you go.

2. Traverse the right subtree recursively, counting the nodes as you go.

3. If you have visited n nodes, return the value of the current node.

4. If you haven't visited n nodes yet, increment the node count and continue to the parent node.

5. If you reach the root node and still haven't visited n nodes, then the n-th node does not exist in the tree.

Note that in a binary tree, each node has at most two children, which means that the time complexity of this algorithm is O(n), where n is the number of nodes in the tree.