hdu4607 Park Visit (树直径)

题意：一棵树，问从任意点出发，每次访问k个点走过的最少的边数

#include <iostream>
#include <algorithm>
#include <cstring>
#include <cstdio>
#define MAXN 200010
#define MAXM 200010
#define INF 0x1f1f1f1f
using namespace std;
int n, m;
struct EDGE
{
    int v, next;
    int w;
}edge[MAXN];
int head[MAXN], e;
int q[MAXN], vis[MAXN];
long long d[MAXN];
void init()
{
    e = 0;
    memset(head, -1, sizeof(head));
}
void add(int u, int v, int w)
{
    edge[e].v = v;
    edge[e].w = w;
    edge[e].next = head[u];
    head[u] = e++;
}
void bfs(int src)
{
    for(int i = 1; i <= n; i++) {vis[i] = 0, d[i] = INF;}
    int h = 0, t = 0;
    q[t++] = src;
    vis[src] = 1;
    d[src] = 0;
    while(h < t)
    {
        int u = q[h++];
        for(int i = head[u]; i != -1; i = edge[i].next)
        {
            int v = edge[i].v;
            int w = edge[i].w;
            if(d[u] + w < d[v])
            {
                d[v] = d[u] + w;
                if(!vis[v])
                {
                    q[t++] = v;
                    vis[v] = 1;
                }
            }
        }
    }
}
int main(){
    int u,v,w,i;
    int t;
    scanf("%d", &t);
    while(t--) {
        scanf("%d%d",&n,&m);
        init();
        for(int i = 1; i <= n-1; i++){
            scanf("%d%d",&u, &v);
            add(u,v,1);
            add(v,u,1);
        }
        bfs(1);
        int pos = -1;
        int mx = -1;
        for(int i = 1; i <= n; i++)
            if(d[i]>mx&&d[i]<INF){
                mx=d[i];
                pos=i;
            }
        bfs(pos);
        int res= -1;
        for(int i=1;i<=n;i++)
            if(d[i]>res&&d[i]<INF){
                res=d[i];
            }
        int Q;
        while(m--){
            scanf("%d",&Q);
            Q--;
            if(Q<=res)printf("%d\n",Q);
            else printf("%d\n",res+(Q-res)*2);
        }
    }
    return 0;
}