New answers tagged counting
1
The provided editorial is so hard to read. My solution is similar (or not?) to the provided one, but easier to understand.
Let $dp(u, i)$ be the number of topological sorts of subtree rooted at node $u$ such that node $u$ is placed at $i$-th position. The definition of $X$ and $Y$ are the same as the definition provided above.
Note that all the $X$ nodes has ...
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