Problem E
The Cat Empire
Languages
en
sv
A continent consists of $N$ different city-states. Exactly $N - 1$ pairs of city-states are directly connected by a trade route, in such a way that it is possible to travel between all pairs of city-states along a sequence of trade routes.
After centuries of living in harmony and peace, there are now strong tensions between the largest city-state, Katen, and a rival kingdom, Kattago. Katen plans to quickly conquer the other city-states to unite them in their struggle against Kattago.
Katen is about to embark on its first campaign to conquer several city-states to form a union. The union must consist of a connected group of city-states and always includes Katen. This means that it should be possible to travel between every city-state in the union using the trade routes without visiting a city-state outside the union. To simplify their logistics during the campaign, they want the number of frontier states in the union to be as small as possible. A frontier state is a city-state that is directly connected to exactly one other city-state within the union. Katen, however, is never counted as a frontier state.
For each number of city-states $1, 2, \dots , N-1$ that Katen can conquer during a campaign, can you calculate the minimum number of frontier states in the resulting union?
Input
The first line of input contains the integer $N$ ($2 \leq N \leq 100,000$), the number of city-states on the continent.
The next $N - 1$ lines describe the trade routes. Let all city-states be numbered $0$, $1$, $\dots $, $N - 1$, where Katen is city-state $0$. Each line contains two integers $a$ and $b$ ($0 \leq a, b < N$, $a \neq b$), the names of two city-states directly connected by a trade route.
Output
On a single line, print the smallest number of frontier states in a union with $1$, $2$, $\dots $, $N - 1$ conquered city-states.
Scoring
Your solution will be tested on a set of test groups, each worth a number of points. Each test group contains a set of test cases. To get the points for a test group you need to solve all test cases in the test group.
Group |
Points |
Constraints |
$1$ |
$21$ |
All city-states, except Katen, are connected by at most $2$ trade routes. |
$2$ |
$28$ |
$N \le 1000$ |
$3$ |
$51$ |
No additional constraints. |
Explanation of sample
In the first example, Katen can conquer, for example, city-states $1$ and $3$ in a campaign. Then, only city-state $3$ is a frontier state, because city-state $1$ is directly connected to both Katen and city-state $3$. However, once all $3$ city-states are conquered, both city-states $2$ and $3$ become frontier states.
Sample Input 1 | Sample Output 1 |
---|---|
4 0 1 0 2 1 3 |
1 1 2 |
Sample Input 2 | Sample Output 2 |
---|---|
8 0 1 1 2 2 3 3 4 3 7 2 5 5 6 |
1 1 1 1 2 2 3 |