[51nod1299]监狱逃离

到现在还是不会写系列，直接贴题解了。

http://www.51nod.com/question/index.html#!questionId=1157

#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
#include<queue>
#define ll long long
#define ui unsigned int
using namespace std;
const int maxn=100233;
struct zs{int too,pre;}e[maxn<<1];int tot,last[maxn];
int zt[maxn],deg[maxn];
int i,j,k,n,m,ans;
bool gg[maxn],GG;

int ra,fh;char rx;
inline int read(){
    rx=getchar(),ra=0,fh=1;
    while((rx<'0'||rx>'9')&&rx!='-')rx=getchar();
    if(rx=='-')fh=-1,rx=getchar();
    while(rx>='0'&&rx<='9')ra*=10,ra+=rx-48,rx=getchar();return ra*fh;
}
inline void insert(int a,int b){
    deg[a]++,deg[b]++;
    e[++tot].too=b,e[tot].pre=last[a],last[a]=tot,
    e[++tot].too=a,e[tot].pre=last[b],last[b]=tot;
}
void dfs(int x,int fa){
    zt[x]=1;
    int num[3]={0,0,0};
    for(int i=last[x];i;i=e[i].pre)if(e[i].too!=fa)
        dfs(e[i].too,x),num[zt[e[i].too]]++;
    if(gg[x]&&deg[x]==1)GG=1;
    if(gg[x])zt[x]=2,ans+=num[1];
    else if(num[1]&&num[2])zt[x]=0,ans++;
    else if(num[1]||num[2])zt[x]=num[1]?1:2;
    else if(num[0])zt[x]=0;
//    printf("x:%d   zt:%d\n",x,zt[x]);
}
int main(){
    n=read()+1,m=read();
    for(i=1;i<n;i++)insert(read()+1,read()+1);
    for(i=1;i<=m;i++)gg[read()+1]=1;
    for(i=n;i;i--)if(deg[i]==1){dfs(i,0),ans+=zt[i]==2;break;}
    printf("%d\n",!GG?ans:-1);
}