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Editorial Team
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Asked: 2026-05-26T16:40:22+00:00

Heres the problem, and my attempted solution. My solution: 1. Run a topological sort

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Heres the problem, and my attempted solution.
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My solution:
1. Run a topological sort on the tree, which runs in linear time BigTheta(E+V) where E is the number of edges and V the number of vertices. This puts it in a linked list which also takes constant time.
2. A vertex u would be an ancestor if it has a higher finishing time than vertex v.
3. Look at the 2 vertice’s in the linked list and compare their finishing time and return true or false depending on the result from step 2.

Does this sound correct or am i missing something?

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1 Answer

  1. Editorial Team

    I don’t think your understanding of what “constant time” means is quite correct. “…time BigTheta(E+V) where E is the number of edges and V the number of vertices” is linear time, not constant time.

    Granted, you are allowed to take linear time for the pre-processing, so that’s ok, but how are you going to do your step 3 (“Look at the 2 vertice’s in the linked list”) in constant time?

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