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No.1614 Majority Painting on Tree

レベル : / AI推定難易度 : 2125 / 実行時間制限 : 1ケース 5.000秒 / メモリ制限 : 512 MB / 標準ジャッジ問題
タグ : (AC するまで非表示) / 解いたユーザー数 32
作問者 : ygussany / テスター : tatyam ngtkana
お気に入りにしたユーザー ProblemId : 5951 / 自分の提出
問題文最終更新日: 2022-10-10 01:00:51
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yukicoder contest 305 (順位表) の他の問題:

Problem Statement

T.T. likes trees, and he is going to play by painting each edge of a tree with a color. However, T.T. also likes majority votes, so he wants to paint the edges so that all of the following conditions are satisfied.

  • Each edge is painted with exactly $1$ color.
  • Each color is painted on at least $1$ edge.
  • For each vertex, if there exists a color painted on a majority (strictly more than half) of the edges incident to that vertex, then all edges incident to that vertex are painted with the same color.

Given a tree with $N$ vertices and the number of colors $C$ to use, find the number of such ways to paint the edges. Here, the colors are distinguishable from one another, and $2$ ways of painting are considered different if there exists an edge painted with different colors in them. Since the answer can be very large, output it modulo the prime $998244353$.

Input

$N$ $C$
$A_1\ \ B_1$
$A_2\ \ B_2$
   $\vdots$
$A_{N-1}\ \ B_{N-1}$

  • $2 \le N \le 10^5$
  • $1 \le C \le 256$
  • $1 \le A_i, B_i \le N \ \ (1 \le i \le N - 1)$
  • All input values are integers.
  • The given graph is a tree.
  • The vertices are numbered $1, 2, \dots, N$.
  • The edges are numbered $1, 2, \dots, N - 1$.
  • Edge $i$ connects vertex $A_i$ and vertex $B_i$.

Output

Output the total number of ways to paint the edges satisfying the conditions, modulo $998244353$.

Sample

Sample 1
Input
5 2
1 2
1 3
1 4
1 5
Output
6

Among the edges incident to vertex $1$, of which there are $4$, all conditions are satisfied when $2$ edges each are painted with different colors. There are $\binom{4}{2} = 6$ ways to choose the edges painted with color $1$, so the answer is $6$.

Painting all edges with the same color fails the $2$nd condition, and painting the $2$ colors on $1$ and $3$ edges respectively fails the $3$rd condition.

Sample 2
Input
5 2
1 2
3 2
3 4
5 4
Output
14

Each vertex has at most $2$ incident edges, so the $3$rd condition is satisfied no matter how the edges are painted. Excluding the cases where only $1$ color is used (all edges are painted with the same color), the answer is $2^4 - 2 = 14$.

Sample 3
Input
7 4
1 2
1 3
1 4
2 5
2 6
2 7
Output
816

Sample 4
Input
7 256
1 2
1 3
1 4
2 5
2 6
2 7
Output
0

It is impossible to use all the colors.

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