BZOJ 2599: [IOI2011] Race Divide and Conquer

Record the dep that reaches the center of gravity in each division and conquer, add it to a bucket, without adding a node, check whether the bucket exists, and then add the sum and the answer to take the minimum value

#include <cstdio>
#include <algorithm>
#include <cmath>
#include <cstring>
#include <queue>
#include <iostream>
#include <cstdlib>
using namespace std;
#define N 300505
#define ll long long
struct node
{
    int to,next,val;
}e[N<<1];
int siz[N],dep[N],ans=1<<30,v[N*5],rot,sum,vis[N],mx[N],head[N],cnt,K,n;
ll dis[N];
void add(int x,int y,int z)
{
    e [cnt] .to = y;
    e[cnt].next=head[x];
    e[cnt].val=z;
    head[x]=cnt++;
    return ;
}
void get_root(int x,int from)
{
    you [x] = 1; mx [x] = 0;
    for(int i=head[x];i!=-1;i=e[i].next)
    {
        int to1 = e [i] .to;
        if(!vis[to1]&&to1!=from)
        {
            get_root(to1,x);
            you [x] + = you [to1];
            mx[x]=max(siz[to1],mx[x]);
        }
    }
    mx [x] = max (mx [x], sum-siz [x]);
    if(mx[x]<mx[rot])rot=x;
}
void insert(int x,int from)
{
    if(dis[x]<=K)v[dis[x]]=min(v[dis[x]],dep[x]);
    for(int i=head[x];i!=-1;i=e[i].next)
    {
        int to1 = e [i] .to;
        if(!vis[to1]&&to1!=from)
        {
            insert(to1,x);
        }
    }
}
void clear(int x,int from)
{
    if(dis[x]<=K)v[dis[x]]=1<<30;
    for(int i=head[x];i!=-1;i=e[i].next)
    {
        int to1 = e [i] .to;
        if(!vis[to1]&&to1!=from)
        {
            clear(to1,x);
        }
    }
}
void calc(int x,int from)
{
    if(dis[x]<=K)ans=min(ans,dep[x]+v[K-dis[x]]);
    for(int i=head[x];i!=-1;i=e[i].next)
    {
        int to1 = e [i] .to;
        if(to1!=from&&!vis[to1])
        {
            dep[to1]=dep[x]+1;
            dis [to1] = dis [x] + e [i] .val;
            calc (to1, x);
        }
    }
}
void dfs(int x)
{
    force[x]=1;v[0]=0;
    for(int i=head[x];i!=-1;i=e[i].next)
    {
        int to1 = e [i] .to;
        if(!vis[to1])
        {
            dep [to1] = 1, dis [to1] = e [i] .val;
            calc (to1.0);
            insert(to1,0);
        }
    }
    for(int i=head[x];i!=-1;i=e[i].next)
    {
        int to1 = e [i] .to;
        if(!vis[to1])
        {
            clear(to1,0);
        }
    }
    for(int i=head[x];i!=-1;i=e[i].next)
    {
        int to1 = e [i] .to;
        if(!vis[to1])
        {
            sum = siz [to1]; rot = 0;
            get_root(to1,0);
            dfs(rot);
        }
    }
}
intmain()
{
    memset(head,-1,sizeof(head));
    scanf("%d%d",&n,&K);
    for(int i=1;i<n;i++)
    {
        int x,y,z;
        scanf("%d%d%d",&x,&y,&z);
        add(x+1,y+1,z);
        add(y+1,x+1,z);
    }
    for(int i=1;i<=K;i++)v[i]=1<<30;
    mx[0]=sum=n;
    get_root(1,0);
    dfs(rot);
    if(ans==1<<30)
    {
        puts("-1");
        return 0;
    }
    printf("%d\n",ans);
    return 0;
}