POJ-3107 Godfather & POJ-2378 Tree Cutting（树的重心）

题目：http://poj.org/problem?id=3107
题意：给你一棵树，让你找到结点，使得剩下的联通块中的结点数量最大的尽量小
即树的重心的定义https://baike.baidu.com/item/%E6%A0%91%E7%9A%84%E9%87%8D%E5%BF%83/20416316?fr=aladdin
思路：直接dfs找其子树的max(结点数量,n-结点数量)
这个题卡vector（而且poj竟然不支持auto
代码：

#include<iostream>#include<cstdio>#include<cstring>#include<algorithm>#include<vector>using namespace std;typedef long long ll;const int N = 5e4+5;struct edge{    int to,nxt;    edge(int t = 0,int n = 0):to(t),nxt(n){}}E[N*2];int n,tot,head[N*2];int dp[N],num[N],pos[N],cnt,minn;void add_edge(int u,int v){    E[tot] = edge(v,head[u]);    head[u] = tot++;}void dfs(int u,int fa){    num[u] = 1;    for(int i = head[u];~i;i = E[i].nxt)    {        int v = E[i].to;        if(v == fa)            continue;        dfs(v,u);        num[u] += num[v];        dp[u] = max(dp[u],num[v]);    }    dp[u] = max(dp[u],n-num[u]);    if(dp[u] < minn)    {        minn = dp[u];        cnt = 0;        pos[cnt++] = u;    }    else if(dp[u] == minn)        pos[cnt++] = u;}int main(){    tot = 0;    memset(head,-1,sizeof(head));    scanf("%d",&n);    int u,v;    for(int i = 1;i < n;i++)    {        scanf("%d%d",&u,&v);        add_edge(u,v);        add_edge(v,u);    }    cnt = 0;    minn = 50000;    dfs(1,-1);    sort(pos,pos+cnt);    printf("%d",pos[0]);    for(int i = 1;i < cnt;i++)        printf(" %d",pos[i]);    printf("\n");    return 0;}