No.3222 Let the World Forget Me
Story
"May the world... please forget me..."
Problem Statement
There is a tree with $N$ vertices, numbered $1, 2, \cdots, N$. The $i$-th edge connects vertex $A_i$ and vertex $B_i$.
Each vertex has a value called its purity; the purity of vertex $i$ is $P_i$.
Currently, some vertices of this tree are contaminated. At time $0$, the contaminated vertices are the $M$ vertices $C_1, C_2, \cdots, C_M$.
From now on, at each time represented as time $t$ for a positive integer $t$, the following event occurs.
- Let $S$ be the set of vertices that are contaminated at that moment. For every $x\in S$, all vertices adjacent to vertex $x$ that are not yet contaminated become contaminated.
In addition, at each time represented as time $t-0.5$ for a positive integer $t$, you perform the following action.
- If there exist vertices that are leaves and are not contaminated at that moment, choose the one with the maximum purity among them, and remove the chosen vertex and the $1$ edge coming out of it. If no such leaf exists, do nothing.
Find the sum of the purity over all vertices you remove at or before time $10^{100}$.
Input
$N\ M$
$P_1\ P_2\cdots\ P_N$
$A_1\ B_1$
$A_2\ B_2$
$\vdots$
$A_{N-1}\ B_{N-1}$
$C_1\ C_2\ \cdots\ C_M$
- $2\leq N\leq 10^5$
- $1\leq M\leq N$
- $1\leq P_i\leq 10^9$
- $P_1, P_2, \cdots, P_N$ are pairwise distinct.
- $1\leq A_i, B_i\leq N$
- $1\leq C_i\leq N$
- The values in $C$ are pairwise distinct.
- All input values are integers.
Output
Let $S$ be the sum of the purity over all vertices you remove at or before time $10^{100}$. Output it on one line in the following format.
$S$
Print a newline at the end.
Sample
Sample 1
Input
5 1 3 2 4 1 5 1 2 1 3 3 4 3 5 1
Output
6
The process proceeds as follows.
- Time $0.5$: Remove vertex $5$.
- Time $1$: Vertices $2$ and $3$ become newly contaminated.
- Time $1.5$: Remove vertex $4$.
- Time $2$ and later: Since all vertices are contaminated, no vertex becomes newly contaminated and no vertex can be removed.
Therefore, the answer is $P_5+P_4=6$.
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