树形DP Choosing Capital for Treeland

给你一棵有向树，需要选定一个点为capital，满足翻转边数最小

思路:先求出1为capital 的答案，然后向下更新孩子节点

dp[i]=dp[i-1]+judge(i);

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<queue>
#include<stack>
#include<vector>
#include<set>
#include<map>  

#define L(x) (x<<1)
#define R(x) (x<<1|1)
#define MID(x,y) ((x+y)>>1)  

#define bug printf("hihi\n")  

#define eps 1e-8
typedef __int64 ll;  

using namespace std;
#define INF 0x3f3f3f3f
#define N 200005  

int dp[N];
int n;  

struct stud{
  int to,ne,len;
}e[N*];
int head[N];
int num;  

inline void add(int u,int v,int len)
{
    e[num].to=v;
    e[num].len=len;
    e[num].ne=head[u];
    head[u]=num++;
}  

void dfs(int u,int pre)
{
    dp[u]=;
    for(int i=head[u];i!=-;i=e[i].ne)
    {
        int to=e[i].to;
        if(to==pre) continue;
        dfs(to,u);
        dp[u]+=dp[to]+e[i].len;
    }
}  

void dfsup(int u,int pre)
{
    for(int i=head[u];i!=-;i=e[i].ne)
    {
        int to=e[i].to;
        if(to==pre) continue;
        dp[to]=dp[u];
        if(e[i].len) dp[to]--;
        else dp[to]++;
        dfsup(to,u);
    }
}  

int main()
{
    int i,j;
    while(~scanf("%d",&n))
    {
        memset(head,-,sizeof(head));
        num=;
        int u,v;
        i=n-;
        while(i--)
        {
            scanf("%d%d",&u,&v);
            add(u,v,);
            add(v,u,);
        }
        dfs(,-);
        dfsup(,-);
        int ans=INF;
        for(i=;i<=n;i++)
            ans=min(ans,dp[i]);
        printf("%d\n",ans);
        vector<int>temp;
        temp.clear();
        for(i=;i<=n;i++)
            if(dp[i]==ans) temp.push_back(i);
        for(i=;i<temp.size();i++)
        {
            if(i) printf(" ");
            printf("%d",temp[i]);
        }
        printf("\n");
    }
    return ;
}