No.1582 Vertexes vs Edges
タグ : / 解いたユーザー数 82
作問者 :
magsta
/ テスター :
butsurizuki
Problem Statement
You are given a tree with $N$ vertices. The vertices of the tree are numbered from $1$ to $N$, and the edges are numbered up to $N-1$.
Edge $i$ connects vertices $u_i, v_i$. Initially, all vertices are painted white.
A-kun and B-kun play a game using this tree.
A-kun performs A-kun's operation below, and B-kun performs B-kun's operation below. The two of them perform these operations alternately. A-kun goes first.
A-kun's operation
Choose one edge whose 2 connected vertices are both painted white, and paint both of those vertices black.
B-kun's operation
Choose one vertex painted black, and paint that vertex white.
These operations are repeated alternately until A-kun can no longer perform his operation (that is, when, at the time A-kun is to perform his operation, there is no edge whose 2 connected vertices are both painted white).
A-kun tries to make the final number of vertices painted black as large as possible, and B-kun tries to make the final number of vertices painted white as large as possible.
Find the number of vertices that are painted black in the end.
Input
$N$
$u_1\ \ v_1$
$u_2\ \ v_2$
$:$
$u_{N-1}\ \ v_{N-1}$
- $2 \leq N \leq 10^5$
- $1 \leq u_i, v_i \leq N$
- $u_i \neq v_i$
- All input values are integers
- The graph represented by the input is a tree
Output
Print the computed value, followed by a newline.
Sample
Sample 1
Input
4 1 2 1 3 1 4
Output
1
First, with A-kun's first operation, vertex 1 and one other vertex are always painted black.
In B-kun's next operation, he paints the black vertex that is not vertex 1 white.
Then A-kun can no longer perform his operation, and the final number of vertices painted black is 1.
Also, if B-kun paints a vertex other than vertex 1 white in his operation, the final number of vertices painted black becomes 2 or more.
Therefore, the answer is 1.
Sample 2
Input
2 1 2
Output
1
Sample 3
Input
12 1 7 8 2 3 12 6 7 7 11 9 1 4 10 12 2 10 1 1 2 5 10
Output
5
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