解题：ZJOI 2015 幻想乡战略游戏

题面

神**所有点都爆int，我还以为我写出什么大锅了，不开long long见祖宗。。。

动态点分治利用点分树树高不超过log的性质，我们对每个点维护一个子树和，一个点分树子树和，一个点分树上父亲的子树和。修改直接爬点分树，查询在点分树上往答案较小的儿子上跳，如果儿子都不如自己优说明自己就是最优的

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int N=100005,inf=1e9;
int n,c,T,t1,t2,t3,cnt,Cnt,sizz;
int p[N],noww[2*N],goal[2*N],val[2*N];
int siz[N],dep[N],far[N],imp[N],top[N],dis[N];
int P[N],Noww[2*N],Goal[2*N],Val[2*N];
int sze[N],maxx[N],vis[N],fer[N];
long long sum[N],dst[N][2];
void Link(int f,int t,int v)
{
    noww[++cnt]=p[f],p[f]=cnt;
    goal[cnt]=t,val[cnt]=v;
    noww[++cnt]=p[t],p[t]=cnt;
    goal[cnt]=f,val[cnt]=v;
}
void Linka(int f,int t,int v)
{
    Noww[++Cnt]=P[f],P[f]=Cnt;
    Goal[Cnt]=t,Val[Cnt]=v;
    Noww[++Cnt]=P[t],P[t]=Cnt;
    Goal[Cnt]=f,Val[Cnt]=v;
}
void DFS(int nde,int fth,int dth)
{
    int tmp=0;
    siz[nde]=1,far[nde]=fth,dep[nde]=dth;
    for(int i=p[nde];i;i=noww[i])
        if(goal[i]!=fth)
        {
            dis[goal[i]]=dis[nde]+val[i];
            DFS(goal[i],nde,dth+1);
            siz[nde]+=siz[goal[i]];
            if(siz[goal[i]]>tmp)
                tmp=siz[goal[i]],imp[nde]=goal[i];
        }
}
void Gettop(int nde,int tpp)
{
    top[nde]=tpp;
    if(imp[nde])
    {
        Gettop(imp[nde],tpp);
        for(int i=p[nde];i;i=noww[i])
            if(goal[i]!=far[nde]&&goal[i]!=imp[nde])
                Gettop(goal[i],goal[i]);
    }
}
int LCA(int x,int y)
{
    while(top[x]!=top[y])
    {
        if(dep[top[x]]<dep[top[y]])
            swap(x,y); x=far[top[x]];
    }
    return dep[x]<dep[y]?x:y;
}
long long Dist(int x,int y)
{
    int lca=LCA(x,y);
    return dis[x]+dis[y]-2*dis[lca];
}
void Mark(int nde,int fth)
{
    sze[nde]=1,maxx[nde]=0;
    for(int i=p[nde];i;i=noww[i])
        if(goal[i]!=fth&&!vis[goal[i]])
        {
            Mark(goal[i],nde);
            sze[nde]+=sze[goal[i]];
            maxx[nde]=max(maxx[nde],sze[goal[i]]);
        }
    maxx[nde]=max(maxx[nde],sizz-sze[nde]);
    if(maxx[nde]<maxx[c]) c=nde;
}
void Create(int nde,int fth)
{
    vis[nde]=true,fer[nde]=fth;
    for(int i=p[nde];i;i=noww[i])
        if(!vis[goal[i]])
        {
            sizz=sze[goal[i]],maxx[c=0]=sze[goal[i]];
            Mark(goal[i],0),Linka(nde,c,goal[i]),Create(c,nde);
        }
}
void Change(int nde,int tsk)
{
    sum[nde]+=tsk; int mem=nde;
    while(fer[nde])
    {
        long long dist=Dist(fer[nde],mem)*tsk;
        dst[fer[nde]][0]+=dist,dst[nde][1]+=dist;
        sum[fer[nde]]+=tsk,nde=fer[nde]; 
    }
}
long long Getans(int nde)
{
    long long ret=dst[nde][0]; int mem=nde;
    while(fer[nde])
    {
        long long dist=Dist(fer[nde],mem);
        ret+=dst[fer[nde]][0]-dst[nde][1];
        ret+=dist*(sum[fer[nde]]-sum[nde]);
        nde=fer[nde];
    }
    return ret;
}
long long Query(int nde)
{
    long long ret=Getans(nde);
    for(int i=P[nde];i;i=Noww[i])
        if(Getans(Val[i])<ret)
            return Query(Goal[i]);
    return ret;
}
int main()
{
    scanf("%d%d",&n,&T);
    for(int i=1;i<n;i++)
        scanf("%d%d%d",&t1,&t2,&t3),Link(t1,t2,t3);
    DFS(1,0,1),Gettop(1,1);
    sizz=n,maxx[c=0]=n,Mark(1,0);
    int mem=c; Create(c,0),c=mem;
    while(T--)
    {
        scanf("%d%d",&t1,&t2);
        Change(t1,t2),printf("%lld
",Query(c)); 
    }
    return 0;
}