Codeforces Round 782 (Div. 2)
E
AND-MEX Walk
Codeforces
2200
原题
← DF →
翻译中…

There is an undirected, connected graph with $n$ vertices and $m$ weighted edges. A walk from vertex $u$ to vertex $v$ is defined as a sequence of vertices $p_1,p_2,\ldots,p_k$ (which are not necessarily distinct) starting with $u$ and ending with $v$, such that $p_i$ and $p_{i+1}$ are connected by an edge for $1 \leq i \lt k$.

翻译中…

We define the length of a walk as follows: take the ordered sequence of edges and write down the weights on each of them in an array. Now, write down the bitwise AND of every nonempty prefix of this array. The length of the walk is the MEX of all these values.

翻译中…

More formally, let us have $[w_1,w_2,\ldots,w_{k-1}]$ where $w_i$ is the weight of the edge between $p_i$ and $p_{i+1}$. Then the length of the walk is given by $\mathrm{MEX}(\{w_1,\,w_1\& w_2,\,\ldots,\,w_1\& w_2\& \ldots\& w_{k-1}\})$, where $\&$ denotes the bitwise AND operation.

翻译中…

Now you must process $q$ queries of the form u v. For each query, find the minimum possible length of a walk from $u$ to $v$.

翻译中…

The MEX (minimum excluded) of a set is the smallest non-negative integer that does not belong to the set. For instance:

翻译中…
  • The MEX of $\{2,1\}$ is $0$, because $0$ does not belong to the set.
  • The MEX of $\{3,1,0\}$ is $2$, because $0$ and $1$ belong to the set, but $2$ does not.
  • The MEX of $\{0,3,1,2\}$ is $4$ because $0$, $1$, $2$ and $3$ belong to the set, but $4$ does not.
翻译中…

Input

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The first line contains two integers $n$ and $m$ ($2 \leq n \leq 10^5$; $n-1 \leq m \leq \min{\left(\frac{n(n-1)}{2},10^5\right)}$).

翻译中…

Each of the next $m$ lines contains three integers $a$, $b$, and $w$ ($1 \leq a, b \leq n$, $a \neq b$; $0 \leq w \lt 2^{30}$) indicating an undirected edge between vertex $a$ and vertex $b$ with weight $w$. The input will not contain self-loops or duplicate edges, and the provided graph will be connected.

翻译中…

The next line contains a single integer $q$ ($1 \leq q \leq 10^5$).

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Each of the next $q$ lines contains two integers $u$ and $v$ ($1 \leq u, v \leq n$, $u \neq v$), the description of each query.

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Output

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For each query, print one line containing a single integer — the answer to the query.

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Note

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The following is an explanation of the first example.

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image The graph in the first example.

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Here is one possible walk for the first query:

翻译中…

$$1 \overset{5}{\rightarrow} 3 \overset{3}{\rightarrow} 2 \overset{1}{\rightarrow} 1 \overset{5}{\rightarrow} 3 \overset{1}{\rightarrow} 4 \overset{2}{\rightarrow} 5.$$

翻译中…

The array of weights is $w=[5,3,1,5,1,2]$. Now if we take the bitwise AND of every prefix of this array, we get the set $\{5,1,0\}$. The MEX of this set is $2$. We cannot get a walk with a smaller length (as defined in the statement).

翻译中…

样例

Input #1
6 7
1 2 1
2 3 3
3 1 5
4 5 2
5 6 4
6 4 6
3 4 1
3
1 5
1 2
5 3
Output #1
2
0
1
InputCopy OutputCopy
Input #2
9 8
1 2 5
2 3 11
3 4 10
3 5 10
5 6 2
5 7 1
7 8 5
7 9 5
10
5 7
2 5
7 1
6 4
5 2
7 6
4 1
6 2
4 7
2 8
Output #2
0
0
2
0
0
2
1
0
1
1
InputCopy OutputCopy
题目信息
题号
1659E
时间限制
3 s
内存限制
256 MB
标签
位运算
暴力
构造
DFS 及类似
并查集
图论

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