POJ 2378 Tree Cutting(树形DP，水)

题意：给出一棵树（n个节点)，去掉一个点后，每个子树的节点数都不大于 n/2,求出这样的节点并按升序输出

树形dp，很神圣的样子，就是树形dfs嘛。。。

代码：

#include<iostream>
#include<cstdio>
#include<string>
#include<cstring>
#include<cmath>
#include<algorithm>
#define nMAX 10010
using namespace std;
int head[nMAX],dp[nMAX];
int s_edge,n,num,ans[nMAX];
struct Edge
{
    int u,v,nxt;
}edge[nMAX*2];
void addedge(int u,int v)
{
    s_edge++;
    edge[s_edge].v=v;
    edge[s_edge].nxt=head[u];
    head[u]=s_edge;
}
int max(int a,int b)
{
    return a>b?a:b;
}
int dfs(int u,int father)
{
    int cnt=1,SUM=0;
    for(int e=head[u];e;e=edge[e].nxt)
    {
        int v=edge[e].v;
        if(v==father)continue;
        int son=dfs(v,u);
        SUM=max(son,SUM);
        cnt+=son;
    }
    SUM=max(SUM,n-cnt);
    if(SUM<=n/2){ans[num++]=u;}
    return cnt;
}
int main()
{
    int i,j,k;
    while(~scanf("%d",&n))
    {
        memset(head,0,sizeof(head));
        s_edge=0;
        for(k=1;k<n;k++)
        {
            scanf("%d%d",&i,&j);
            addedge(i,j);
            addedge(j,i);
        }
        memset(dp,0,sizeof(dp));
        num=0;
        dfs(1,0);
        if(num==0){printf("NONE\n");continue;}
        sort(ans,ans+num);
        for(i=0;i<num;i++)
            printf("%d\n",ans[i]);
    }
    return 0;
}