Codeforces Round 845 (Div. 2) and ByteRace 2023
D
Score of a Tree
Codeforces
1900
原题
← CE →
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You are given a tree of $n$ nodes, rooted at $1$. Every node has a value of either $0$ or $1$ at time $t=0$.

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At any integer time $t \gt 0$, the value of a node becomes the bitwise XOR of the values of its children at time $t - 1$; the values of leaves become $0$ since they don't have any children.

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Let $S(t)$ denote the sum of values of all nodes at time $t$.

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Let $F(A)$ denote the sum of $S(t)$ across all values of $t$ such that $0 \le t \le 10^{100}$, where $A$ is the initial assignment of $0$s and $1$s in the tree.

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The task is to find the sum of $F(A)$ for all $2^n$ initial configurations of $0$s and $1$s in the tree. Print the sum modulo $10^9+7$.

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Input

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Each test contains multiple test cases. The first line contains the number of test cases $t$ ($1 \le t \le 10^5$). The description of the test cases follows.

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The first line of each test case contains $n$ ($1 \le n \le 2 \cdot 10^5$) — the number of nodes in the tree.

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The next $n-1$ lines of each test case contain two integers each — $u$, $v$ indicating an edge between $u$ and $v$ ($1 \le u, v \le n$).

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It is guaranteed that the sum of $n$ over all test cases does not exceed $2 \cdot 10^5$.

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Output

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Output the sum modulo $10^9+7$ for each test case.

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Note

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Let us find $F(A)$ for the configuration $A = [0,1,0,0,1,1]$ ($A[i]$ denotes the value of node $i$). Initially (at $t = 0$) our tree is as shown in the picture below. In each node, two values are shown: the number and the value of this node. $S(0)$ for this configuration is $3$.

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image

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At $t = 1$ the configuration changes to $[1,0,0,0,0,0]$. The tree looks as shown below. $S(1) = 1$.

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image

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At $t = 2$ the configuration changes to $[0,0,0,0,0,0]$. The tree looks as shown below. $S(2) = 0$.

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image

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For all $t \gt 2$, the graph remains unchanged, so $S(t)=0$ for all $t \gt 2$. So, for the initial configuration $A = [0,1,0,0,1,1]$, the value of $F(A) = 3 + 1 = 4$.

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Doing this process for all possible $2^{6}$ configurations yields us an answer of $\textbf{288}$.

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样例

Input #1
1
6
1 2
1 3
3 4
3 5
3 6
Output #1
288
InputCopy OutputCopy
题目信息
题号
1777D
时间限制
2 s
内存限制
512 MB
标签
位运算
组合数学
DFS 及类似
动态规划
数学
概率论
树

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