POJ-2378 Tree Cutting

题目大意：一棵n个节点的树，找出所有的点满足：删除它之后，产生的最大（这里节点数最多即为最大）新树中节点数不超n的一半。

题目分析：两次深搜，过程类似求重心。

 

代码如下：

# include<iostream>
# include<cstdio>
# include<cstring>
# include<vector>
# include<queue>
# include<list>
# include<set>
# include<map>
# include<string>
# include<cmath>
# include<cstdlib>
# include<algorithm>
using namespace std;
# define LL long long

const int N=1005;
const int INF=1000000000;

vector<int>e[N*10];
int size[N*10];
int n,dp[N*10];

void init()
{
	for(int i=1;i<=n;++i)
		e[i].clear();
	int a,b;
	for(int i=1;i<n;++i){
		scanf("%d%d",&a,&b);
		e[a].push_back(b);
		e[b].push_back(a);
	}
}

void dfs(int u,int fa)
{
	size[u]=1;
	for(int i=0;i<e[u].size();++i){
		int v=e[u][i];
		if(v==fa) continue;
		dfs(v,u);
		size[u]+=size[v];
	}
}

void dfs1(int u,int fa)
{
	dp[u]=n-size[u];
	for(int i=0;i<e[u].size();++i){
		int v=e[u][i];
		if(v==fa) continue;
		dp[u]=max(dp[u],size[v]);
		dfs1(v,u);
	}
}

void solve()
{
	dfs(1,-1);
	dfs1(1,-1);
	bool flag=true;
	for(int i=1;i<=n;++i){
		if(dp[i]<=n/2){
			printf("%d\n",i);
			flag=false;
		}
	}
	if(flag) printf("NONE\n");
}

int main()
{
	while(~scanf("%d",&n))
	{
		init();
		solve();
	}
	return 0;
}