hdu 4607 Park Visit (dfs)

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=4607

首先如果k小于等于直径长度，那么答案为k−1。如果k大于直径长度，设直径长度为r，那么答案为r−1+(k−r)∗2。

#include <cstdio>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <cstring>
#include <queue>
#include <vector>
#define maxn 105000
using namespace std;

const int INF = 0x3f3f3f;

vector<int> G[maxn];
int N,M;
int maxdeep,point;
bool vis[maxn];
void dfs(int u,int deep){
    if(maxdeep < deep){
        maxdeep = deep;
        point = u;
    }
    for(int i=0;i<G[u].size();i++){
       int v = G[u][i];  
       if(!vis[v]){
         vis[v] = true;   //printf("u,v  %d %d
",u,v);jf
         dfs(v,deep+1);
       }
    }
}

int main()
{
    //if(freopen("input.txt","r",stdin)== NULL)  {printf("Error
"); exit(0);}

    int T;
    cin>>T;
    while(T--){
        cin>>N>>M;
        if(N == 1){
            for(int i=1;i<=M;i++){
                int K;
             scanf("%d",&K);
             printf("0
");
               } 
            continue;       
        } 
          
        for(int i=1;i<=N;i++)   G[i].clear();
        for(int i=1;i<=N-1;i++){
            int a,b;
            scanf("%d %d",&a,&b);
            G[a].push_back(b);
            G[b].push_back(a);
        }
        memset(vis,0,sizeof(vis));
        maxdeep = 0; point = 0;
        vis[1] = true;
        dfs(1,0);
        memset(vis,0,sizeof(vis));
        dfs(point,0);
        for(int i=1;i<=M;i++){
            int K;
            scanf("%d",&K);
            if(maxdeep >= K-1) printf("%d
",K-1);
            else           printf("%d
",maxdeep + 2 * (K - 1 - maxdeep));
        }
    }
}