hdu 4607 Park Visit 树的直径

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
using namespace std;
#define maxn 100100
#define maxm 210000
struct Node
{
    int u,v,next;
}e[maxm];
int head[maxn],cnt,w[maxn],s,maxlen;
bool vis[maxn];
void add(int u,int v)
{
    e[cnt].u=u;
    e[cnt].v=v;
    e[cnt].next=head[u];
    head[u]=cnt++;
    e[cnt].u=v;
    e[cnt].v=u;
    e[cnt].next=head[v];
    head[v]=cnt++;
}

void bfs(int u)
{
    queue <int> Q;
    memset(vis,0,sizeof(vis));
    vis[u]=1;
    w[u]=0;
    s=u;
    Q.push(u);
    while(!Q.empty())
    {
        int x=Q.front();
        Q.pop();
        for(int i=head[x];i!=-1;i=e[i].next)
        {
            int v=e[i].v;
            if(vis[v]) continue;
            vis[v]=1;
            w[v]=w[x]+1;
            Q.push(v);
            if(w[v]>maxlen)
            {
                s=v;
                maxlen=w[v];
            }
        }
    }
}
int main()
{
    int cas,n,m,k;
    scanf("%d",&cas);
    while(cas--)
    {
        int i,u,v;
        scanf("%d%d",&n,&m);
        memset(head,-1,sizeof(head));
        cnt=0;
        for(i=1;i<n;i++)
        {
            scanf("%d%d",&u,&v);
            add(u,v);
        }
        maxlen=-1;
        bfs(1);
        maxlen=-1;
        bfs(s);
        for(i=1;i<=m;i++)
        {
            scanf("%d",&k);
            if(k<=maxlen+1) printf("%d\n",k-1);
            else printf("%d\n",maxlen+2*(k-maxlen-1));
        }
    }
    return 0;
}