Leetcode 1719. Number Of Ways To Reconstruct A Tree

Given unordered pairs that specify exactly which node pairs are in an ancestor-descendant relationship (a pair exists iff one node is an ancestor of the other), determine whether there are 0, 1, or multiple rooted trees that realize those ancestor relations. The core challenge is to infer consistent parent-child assignments (and detect contradictions or ambiguity) from the global comparability information.