Codeforces Round 439 (Div. 2)
D
The Overdosing Ubiquity
Codeforces
2800
原题
← CE →
翻译中…

The fundamental prerequisite for justice is not to be correct, but to be strong. That's why justice is always the victor.

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The Cinderswarm Bee. Koyomi knows it.

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The bees, according to their nature, live in a tree. To be more specific, a complete binary tree with $*n*$ nodes numbered from $1$ to $*n*$. The node numbered $1$ is the root, and the parent of the $*i*$-th ($2 ≤ *i* ≤ *n*$) node is image. Note that, however, all edges in the tree are undirected.

翻译中…

Koyomi adds $*m*$ extra undirected edges to the tree, creating more complication to trick the bees. And you're here to count the number of simple paths in the resulting graph, modulo $10^{9} + 7$. A simple path is an alternating sequence of adjacent nodes and undirected edges, which begins and ends with nodes and does not contain any node more than once. Do note that a single node is also considered a valid simple path under this definition. Please refer to the examples and notes below for instances.

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Input

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The first line of input contains two space-separated integers $*n*$ and $*m*$ ($1 ≤ *n* ≤ 10^{9}$, $0 ≤ *m* ≤ 4$) — the number of nodes in the tree and the number of extra edges respectively.

翻译中…

The following $*m*$ lines each contains two space-separated integers $*u*$ and $*v*$ ($1 ≤ *u*, *v* ≤ *n*$, $*u* ≠ *v*$) — describing an undirected extra edge whose endpoints are $*u*$ and $*v*$.

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Note that there may be multiple edges between nodes in the resulting graph.

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Output

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Output one integer — the number of simple paths in the resulting graph, modulo $10^{9} + 7$.

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Note

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In the first example, the paths are: $(1)$; $(2)$; $(3)$; $(1, 2)$; $(2, 1)$; $(1, 3)$; $(3, 1)$; $(2, 1, 3)$; $(3, 1, 2)$. (For the sake of clarity, the edges between nodes are omitted since there are no multiple edges in this case.)

翻译中…

In the second example, the paths are: $(1)$; $(1, 2)$; $(1, 2, 3)$; $(1, 3)$; $(1, 3, 2)$; and similarly for paths starting with $2$ and $3$. ($5 × 3 = 15$ paths in total.)

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In the third example, the paths are: $(1)$; $(2)$; any undirected edge connecting the two nodes travelled in either direction. ($2 + 5 × 2 = 12$ paths in total.)

翻译中…

样例

Input #1
3 0
Output #1
9
InputCopy OutputCopy
Input #2
3 1
2 3
Output #2
15
InputCopy OutputCopy
Input #3
2 4
1 2
2 1
1 2
2 1
Output #3
12
InputCopy OutputCopy
题目信息
题号
869D
时间限制
1 s
内存限制
256 MB
标签
暴力
DFS 及类似
图论

题面与样例版权归 Codeforces 及出题人所有;中文翻译由 AI 生成(CI 管线),如有出入请以原文为准。