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Asked: 2026-05-13T18:32:32+00:00

Here is a tree: There will be one root. Each tree node has zero

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Here is a tree:

  1. There will be one root.

  2. Each tree node has zero or more children.

  3. It is allowed that two nodes points to the same child. Say, both node A
    and node B has child C.

However, it is prohibited that,

Node A is an offspring of Node B, and
Node B is an offspring of Node A.

One prohibited case is

Node A has a child Node C and Node D,

Both Node C and D has a child node E,

Node E has a child of A.

The question is, how to determine this circle in a fastest manner?

UPDATE: I realize this is to find any cycle in a directed graph. Just now I managed to think out a solution similar to Tarjan’s algorithm.

Thanks for comments.

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1 Answer

  1. Editorial Team

    Do a Depth First Search through the tree. If at any point you find a node that is already in your backtracking stack, there is a circle.

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