codeforces 700B Connecting Universities

Posted 2020-08-12 ziliuziliu

蛮有意思的。。。。考虑每条边的贡献。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxv 200500
#define maxe 400500
using namespace std;
int n,k,x,y,nume=0,g[maxv],size[maxv],fath[maxv];
long long ans=0;
bool vis[maxv];
struct edge
{
    int v,nxt;
}e[maxe];
void addedge(int u,int v)
{
    e[++nume].v=v;
    e[nume].nxt=g[u];
    g[u]=nume;
}
void dfs1(int x)
{
    size[x]=0;
    for (int i=g[x];i;i=e[i].nxt)
    {
        int v=e[i].v;
        if (v!=fath[x])
        {
            fath[v]=x;
            dfs1(v);
            size[x]+=size[v];
        }
    }
    if (vis[x]) size[x]++;
}
void dfs2(int x)
{
    for (int i=g[x];i;i=e[i].nxt)
    {
        int v=e[i].v;
        if (v!=fath[x])
        {
            ans+=min(size[v],2*k-size[v]);
            dfs2(v);
        }
    }
}
int main()
{
    scanf("%d%d",&n,&k);
    for (int i=1;i<=2*k;i++) {scanf("%d",&x);vis[x]=true;}
    for (int i=1;i<=n-1;i++)
    {
        scanf("%d%d",&x,&y);
        addedge(x,y);addedge(y,x);
    }
    dfs1(1);
    dfs2(1);
    printf("%I64d\n",ans);
    return 0;
}