codeforces 700B

在给的点中选出一对对点，让每两个点的距离和最大

乱搞，做过这种关于类型的，这次算比较简单的。

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

using namespace std;
vector<int>edge[200100];
int vis[200100];
int num[200100];
int n,k;
long long ans;
void dfs1(int root,int father)
{
    if (vis[root]) num[root]=1;
    for (int i=0;i<edge[root].size();i++)
    {
        int v=edge[root][i];
        if (v==father) continue;
        dfs1(v,root);
        num[root]+=num[v];
    }
}
void dfs2(int root,int father)
{
    for (int i=0;i<edge[root].size();i++)
    {
        int v=edge[root][i];
        if (v==father) continue;
        ans+=min(num[v],2*k-num[v]);
        dfs2(v,root);
    }
}
int main()
{
    scanf ("%d%d",&n,&k);
    int temp=2*k;
    while (temp--)
    {
        int p;
        scanf ("%d",&p);
        vis[p]=1;
    }
    n--;
    while (n--)
    {
        int t1,t2;
        scanf ("%d%d",&t1,&t2);
        edge[t1].push_back(t2);
        edge[t2].push_back(t1);
    }
    dfs1(1,0);
    dfs2(1,0);
    printf ("%I64d\n",ans);
    return 0;
}