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,0);
    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 != -1; i = edge[i].next)
        {
            if(!vis[edge[i].v])
            {
                q.push(Point(edge[i].v,d+1));
                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 = 0;
        scanf("%d%d",&n,&m);
        memset(vis,0,sizeof(vis));
        memset(edge,0,sizeof(edge));
        memset(head,-1,sizeof(head));
        for(int i = 0 ; i < n-1 ; i++)
        {
            int a,b;
            scanf("%d%d",&a,&b);
            Edge E;
            E.u = a;
            E.v = b;
            add(E);
        }
        int dis1 = bfs(1);
        memset(vis,0,sizeof(vis));
        int dis = bfs(endp);
        for(int i = 0 ; i < m ; i++)
        {
            int k;
            scanf("%d",&k);
            if(k-1 <= dis) printf("%d
",k-1);
            else printf("%d
",dis+2*(k-dis-1));
        }
    }
    return 0;
}