POJ 2378 Tree Cutting(树形DP)

After Farmer John realized that Bessie had installed a "tree-shaped" network among his N (1 <= N <= 10,000) barns at an incredible cost, he sued Bessie to mitigate his losses. 

Bessie, feeling vindictive, decided to sabotage Farmer John‘s network by cutting power to one of the barns (thereby disrupting all the connections involving that barn). When Bessie does this, it breaks the network into smaller pieces, each of which retains full connectivity within itself. In order to be as disruptive as possible, Bessie wants to make sure that each of these pieces connects together no more than half the barns on FJ. 

Please help Bessie determine all of the barns that would be suitable to disconnect.

* Line 1: A single integer, N. The barns are numbered 1..N. 

* Lines 2..N: Each line contains two integers X and Y and represents a connection between barns X and Y.

* Lines 1..?: Each line contains a single integer, the number (from 1..N) of a barn whose removal splits the network into pieces each having at most half the original number of barns. Output the barns in increasing numerical order. If there are no suitable barns, the output should be a single line containing the word "NONE".

10
1 2
2 3
3 4
4 5
6 7
7 8
8 9
9 10
3 8

3
8

INPUT DETAILS: 

The set of connections in the input describes a "tree": it connects all the barns together and contains no cycles. 

OUTPUT DETAILS: 

If barn 3 or barn 8 is removed, then the remaining network will have one piece consisting of 5 barns and two pieces containing 2 barns. If any other barn is removed then at least one of the remaining pieces has size at least 6 (which is more than half of the original number of barns, 5).

DFS建树，对于某一个点有dp[x]代表包括x在内的点的子树点的个数。

若符合条件有：对于x的子节点y:dp[y]<=n/2而且其余点n-dp[x]<=n/2;

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
typedef long long LL;
using namespace std;
#define REPF( i , a , b ) for ( int i = a ; i <= b ; ++ i )
#define REP( i , n ) for ( int i = 0 ; i < n ; ++ i )
#define CLEAR( a , x ) memset ( a , x , sizeof a )
const int maxn=10000+100;
int res[maxn],dp[maxn],vis[maxn];
vector<int>v[maxn];
int n,temp,h;
int dfs(int x)
{
    if(dp[x]>0)   return dp[x];
    dp[x]=1;
    vis[x]=1;
    int flag=1;
    REP(i,v[x].size())
    {
        int y=v[x][i];
        if(vis[y])   continue;
        if(dfs(y)>h)
            flag=0;
        dp[x]+=dfs(y);
    }
    if(flag&&n-dp[x]<=h)
        res[x]=1;
    return dp[x];
}
int main()
{
     int x,y;
     std::ios::sync_with_stdio(false);
     while(cin>>n)
     {
         REPF(i,1,n)   v[i].clear();
         REP(i,n-1)
         {
             cin>>x>>y;
             v[x].push_back(y);
             v[y].push_back(x);
         }
         CLEAR(vis,0);
         CLEAR(res,0);
         h=n/2;
         vis[1]=1;
         int tt=dfs(1);
         REPF(i,1,n)
           if(res[i])   cout<<i<<endl;
     }
     return 0;
}