HDU 4607 Park Visit HDU暑期多校1

10W个点的一棵树,边权为1

求访问K个点要走过的最小路程

BFS求出一条最长路以后,我们可以YY出其他的边都要重复走两次

树上的最长路可以从任意一点开始BFS求出这点的最大距离,再把终点设置为起点再做一次BFS

所以就判断K和最长路间的距离就行了 O(n) 算法

 #include <set>
 #include <map>
 #include <list>
 #include <cmath>
 #include <ctime>
 #include <deque>
 #include <queue>
 #include <stack>
 #include <bitset>
 #include <cstdio>
 #include <string>
 #include <vector>
 #include <cassert>
 #include <cstdlib>
 #include <cstring>
 #include <sstream>
 #include <fstream>
 #include <numeric>
 #include <iomanip>
 #include <iostream>
 #include <algorithm>
 #include <functional>
 using namespace std;
 //typedef long long LL;
 //typedef unsigned long long ULL;
 // typedef __int64 LL;
 // typedef unisigned __int64 ULL;
 #define EPS         1e-8
 #define MAXN        100005
 #define MAXE        200005
 #define INF         0x3f3f3f3f
 #define PI          acos(-1.0)
 #define MOD         1000000007
 #define max(a,b)    ((a) > (b) ? (a) : (b))
 #define min(a,b)    ((a) < (b) ? (a) : (b))
 #define max3(a,b,c) (max(max(a,b),c))
 #define min3(a,b,c) (min(min(a,b),c))
 #define mabs(a)     (((a) < 0) ? (-a) : (a))
 #define YES         cout<<"YES"<<endl;
 #define L(t)        (t << 1)
 #define R(t)        (t << 1 | 1)
 #define Mid(a,b)    ((a+b)>>1)
 #define lowbit(a)   (a&-a)
 #define FOR(a,b,c)  for(int a = b; a < c; a++)
 #define FOR2(a,b,c) for(int a = b; a <= c; a++)
 #define LOOP(a,b)   for(int lop = a; lop < b; lop++)
 #define LOOP2(a,b)  for(int lop = a; lop <= b; lop++)
 //int gcd(int a,int b){ return b?gcd(b,a%b):a; }
 //int lcm(int a,int b){ return a*b/gcd(a,b); }
 struct Edge
 {
     int u,v,w; // st,ed,value
     int next;
 }edge[MAXE];
 struct Point
 {
     int p;
     int dis;
     Point(int a,int b)
     {
         p = a;
         dis = b;
     }
 };
 int head[MAXN];
 bool vis[MAXN];
 int cnt ; // num of edge
 int n ; // num of point
 int m ;
 void add(Edge x)
 {
     edge[cnt].u = x.u;
     edge[cnt].v = x.v;
     edge[cnt].w = x.w;
     edge[cnt].next = head[x.u];
     head[x.u] = cnt++;
     edge[cnt].v = x.u;
     edge[cnt].u = x.v;
     edge[cnt].w = x.w;
     edge[cnt].next = head[x.v];
     head[x.v] = cnt++;
 }
 int endp;
 int bfs(int s)
 {
     int dis = -INF;
     queue<Point> q;
     Point p(s,);
     q.push(p);
     vis[s] = true;
     while(!q.empty())
     {
         int u = q.front().p;
         int d = q.front().dis;
         if(d > dis)
         {
             dis = max(dis,d);
             endp = u;
         }
         for(int i = head[u]; i != -; i = edge[i].next)
         {
             if(!vis[edge[i].v])
             {
                 q.push(Point(edge[i].v,d+));
                 vis[edge[i].v] = true;
             }
         }
         q.pop();
     }
     return dis;
 }
 int main()
 {
     // freopen("in.txt","r",stdin);
     // freopen("out.txt","w",stdout);
     // std::ios::sync_with_stdio(false);
     int t;
     scanf("%d",&t);
     while(t--)
     {
         cnt = ;
         scanf("%d%d",&n,&m);
         memset(vis,,sizeof(vis));
         memset(edge,,sizeof(edge));
         memset(head,-,sizeof(head));
         for(int i =  ; i < n- ; i++)
         {
             int a,b;
             scanf("%d%d",&a,&b);
             Edge E;
             E.u = a;
             E.v = b;
             add(E);
         }
         int dis1 = bfs();
         memset(vis,,sizeof(vis));
         int dis = bfs(endp);
         for(int i =  ; i < m ; i++)
         {
             int k;
             scanf("%d",&k);
             if(k- <= dis) printf("%d\n",k-);
             else printf("%d\n",dis+*(k-dis-));
         }
     }
     return ;
 }