In which traversal does the parent node visit last?

In a postorder traversal, the parent node is indeed the last to be visited. This traversal method processes the left subtree first, followed by the right subtree, and concludes with the parent node itself. This means you traverse all the way down to the leaves of the tree before you visit their parents, ensuring that the parent node is encountered only after both of its children have been fully processed.

This approach is particularly useful in scenarios where you need to evaluate or delete nodes in a way that ensures child nodes are handled before their parents, such as in situations involving tree deletion or mathematical expression evaluation. In contrast, preorder visits the parent first, and inorder visits the parent between its left and right children, thereby ensuring that the parent is not the last to be processed.