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Asked: 2026-05-16T10:52:41+00:00

I understand pre-order, in-order, and post-order tree traversal algorithms just fine. ( Reference ).

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I understand pre-order, in-order, and post-order tree traversal algorithms just fine. (Reference). I understand a few uses: in-order for traversing binary search trees in order, pre-order for cloning a tree. But I can’t for the life of me come up with a real world task that I’d need post-order traversal to accomplish.

Can you give me an example? And: can you give me any better uses for pre-order traversal?

Edit: Can anyone give me an example other than expression trees and RPN? Is that really all post-order is good for?

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1 Answer

  1. Editorial Team

    Topological sorting is a post-order traversal of trees (or directed acyclic graphs).

    The idea is that the nodes of the graph represent tasks and an edge from A to B indicates that A has to be performed before B. A topological sort will arrange these tasks in a sequence such that all the dependencies of a task appear earlier than the task itself. Any build system like UNIX make has to implement this algorithm.

    The example that Dario mentioned — destroying all nodes of a tree with manual memory management — is an instance of this problem. After all, the task of destroying a node depends on the destruction of its children.

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