【POJ】2378 - Tree Cutting 树形dp

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <queue>
#include <vector>
#include <numeric>
#include <algorithm>
using namespace std;

int n;
vector <int> v[10005];
int size[10005],mark[10005];

void dfs(int x,int fx){
size[x]=1;
mark[x]=1;
for (int i=0;i<v[x].size();i++){
int y=v[x][i];
if (y!=fx){
dfs(y,x);
if (size[y]*2>n) mark[x]=0;
size[x]+=size[y];
}
}
if ((n-size[x])*2>n) mark[x]=0;
}

int main(){

while (cin >> n){
for (int i=1;i<n;i++){
int x,y;
cin >> x >> y;
v[x].push_back(y);
v[y].push_back(x);
}
dfs(1,0);
bool flag=1;
for (int i=1;i<=n;i++){
if (mark[i]){
cout << i << endl;
flag=0;
}
}
if (flag) cout << "NONE" << endl;
}
}