No.1215 City Annihilation Beam
タグ : / 解いたユーザー数 8
作問者 :
Problem Statement
There is a country with a tree structure, and the $N$ cities that make up the country are numbered $1, 2, \dots , N$.
The cities are connected by bidirectional highways, and the $i$-th highway connects city $A_i$ and city $B_i$.
This country has $K$ temples; the $i$-th temple is located in city $C_i$ and its value is $D_i$.
The god worshipped by this country is more pleased the larger the value $X$ defined by the following procedure is.
- Let $S$ be the sum of the values of the temples.
- Viewing the country as a tree rooted at city $1$, let city $T$ be the LCA of all cities that have a temple.
- $X$ is $S$ $+$ (the minimum number of roads that must be traversed on the way from city $T$ to city $1$).
- However, if no temples exist, $X$ is $-10^{10^{10}}$.
Fortunately, he can perform the following operation at most $1$ time:
- Choose integers $l$ , $r$ ($1$ $\leq$ $l$ $\leq$ $r$ $\leq$ $K$) and annihilate with a beam all temples whose number (note that this is not the city number) is between $l$ and $r$, inclusive.
Since it was difficult for Paken-kun to figure out the most efficient way to fire the beam, he asked you to find the maximum $X$ achievable by the possible operations.
However, you felt pangs of conscience about annihilating temples, so you decided to compute $X$ for each of all $\frac{K(K+1)}{2}+1$ ways of operating, and then tell Paken-kun the median of these values.
Here, the median refers to the $\left\lfloor \frac{\left(\frac{K(K+1)}{2}+1\right)+1}{2}\right\rfloor$-th smallest value among the values of $X$ achievable by all the ways of operating.
Input
$N\ K$
$C_1\ C_2\ \dots\ C_K$
$D_1\ D_2\ \dots\ D_K$
$A_1\ B_1$
$A_2\ B_2$
$\dots$
$A_{N-1}\ B_{N-1}$
- $2\leq K\leq N\leq 10^5$
- $1\leq C_i\leq N (1\leq i\leq K)$
- $C_i\neq C_j (1\leq i < j\leq K)$
- $-10^9\leq D_i\leq 10^9 (1\leq i\leq K)$
- $1\leq A_i,B_i\leq N (1\leq i\leq N-1)$
- All inputs are integers.
- The graph given in the input is a tree.
Output
Find the median of $X$. Print a newline at the end.
Sample
Sample 1
Input
3 2 2 3 1 1 1 2 2 3
Output
2
The costs for all $4$ ways are $-10^{10^{10}}, 2, 3, 3$, and the median is $2$.
Sample 2
Input
7 3 4 5 7 1 10 100 1 2 2 3 3 4 3 5 1 6 6 7
Output
101
The costs for all $7$ ways are $-10^{10^{10}}, 4, 13, 101, 102, 110, 111$, and the median is $101$.
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