Hello 2026
D1
Tree Coloring (Easy Version)
Codeforces
1500
原题
← CD2 →
翻译中…

This is the Easy version of the problem. The difference between the versions is that in this version, you are only required to find the minimum number of operations. You can hack only if you solved all versions of this problem.

翻译中…

You are given a rooted tree$^{\text{∗}}$ consisting of $n$ vertices numbered from $1$ to $n$, where the root has index $1$, and each vertex is initially white. Define $d_i$ as the distance from the root to the $i$-th vertex. You can perform the following operations any number of times:

翻译中…
  1. Select a subset $S$ of white vertices such that no two nodes in $S$ are connected by an edge, or have the same distance to node $1$. Formally, $S$ should satisfy for all $x,y\in S$ and $x\neq y$, $d_x\neq d_y$ and there are no edges between $x$ and $y$.
  2. Color the vertices in $S$ black.
翻译中…

Your job is to find the minimum number of operations required to color the full tree black.

翻译中…

$^{\text{∗}}$A tree is a connected graph without cycles. A rooted tree is a tree where one vertex is special and called the root.

翻译中…

Input

翻译中…

Each test contains multiple test cases. The first line contains the number of test cases $t$ ($1 \le t \le 10^4$). The description of the test cases follows.

翻译中…

The first line of each test case contains a single integer $n$ ($2\le n\le 2\cdot 10^5$) – the number of vertices in the tree.

翻译中…

The $i$-th following $n-1$ lines contain two integers $u_i$ and $v_i$ ($1\le u_i,v_i\le n$, $u_i\neq v_i$) – the ends of the $i$-th edge.

翻译中…

It is guaranteed that the given edges form a tree.

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It is guaranteed that the sum of $n$ over all test cases doesn't exceed $2\cdot10^5$.

翻译中…

Output

翻译中…

For each test case, output the minimum number of operations on a new line.

翻译中…

Note

翻译中…

In the first test case, $d_1=1$ and $d_2=d_3=d_4=d_5=2$. We can show that we must perform at least $5$ operations because there are no two nodes that can be operated on simultaneously.

翻译中…

In the second test case, we can show that the least number of operations required to color the full tree is $4$. One way to do so is to color nodes $1$ and $3$ in the same operation, and all $3$ other nodes in their own operations.

翻译中…

样例

Input #1
10
5
3 1
1 2
5 1
4 1
5
3 2
2 4
2 5
1 2
5
3 4
4 1
5 1
1 2
5
2 5
3 1
2 1
3 4
5
1 3
1 5
4 3
2 4
13
2 1
3 2
4 2
5 4
6 3
7 1
8 5
9 6
10 4
11 7
12 8
13 10
10
5 7
8 1
1 10
2 8
8 4
9 4
6 1
5 3
7 8
10
7 6
3 7
6 9
7 1
9 8
5 1
3 10
9 2
1 4
10
10 6
2 8
4 10
7 5
1 2
7 10
10 9
9 1
7 3
10
6 8
9 7
4 10
5 9
4 2
3 8
6 5
1 5
1 10
Output #1
5
4
4
3
3
3
4
4
4
3
InputCopy OutputCopy
题目信息
题号
2183D1
所属比赛
时间限制
2 s
内存限制
512 MB
标签
构造
DFS 及类似
贪心
树

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。