bzoj 3653 谈笑风生 题解

#include<bits/stdc++.h>
#define LL long long
using namespace std;
inline int read(){
    int res=0,f=1;char ch=getchar();
    while(!isdigit(ch)) f=ch=='-'?-1:f,ch=getchar();
    while(isdigit(ch)) res=(res<<3)+(res<<1)+(ch&15),ch=getchar();
    return res*f;
}
int n,q,g[300010],cnt,dep[300010],cnd,rt[300010];
LL sz[300010];
int fir[300010],nxt[300010<<1],son[300010<<1],tot;
pair<int,int> id[300010];
struct node{
    int l,r;
LL sum;
}tr[300010<<5];
inline void add(int x,int y){++tot;nxt[tot]=fir[x];fir[x]=tot;son[tot]=y;}
inline void dfs(int x,int fa){
    ++cnt;
    id[x].first=cnt;
    dep[x]=dep[fa]+1;
    sz[x]=1;
    g[cnt]=x;
    for(int to,i=fir[x];i;i=nxt[i]){
        to=son[i];
        if(to==fa) continue ;
        dfs(to,x);
        sz[x]+=sz[to];
    }
    id[x].second=cnt;
}
inline void insert(int &x,int l,int r,int pos,int v){
++cnd;
    tr[cnd]=tr[x];
x=cnd;
    tr[x].sum+=(LL)v;
    if(l==r) return ;
    int mid=l+r>>1;
    if(pos<=mid) insert(tr[x].l,l,mid,pos,v);
    else insert(tr[x].r,mid+1,r,pos,v);
}
inline LL query(int x,int y,int l,int r,int L,int R){
    if(L<=l&&r<=R) return tr[y].sum-tr[x].sum;
    int mid=l+r>>1;
LL res=0;
    if(L<=mid) res+=query(tr[x].l,tr[y].l,l,mid,L,R);
    if(R>mid) res+=query(tr[x].r,tr[y].r,mid+1,r,L,R);
    return res;
}
int main(){
    n=read(),q=read();
    for(int u,v,i=1;i<n;i++){
        u=read(),v=read();
        add(u,v),add(v,u);
    }
    dfs(1,0);
    for(int i=1;i<=n;i++) rt[i]=rt[i-1],insert(rt[i],1,n,dep[g[i]],sz[g[i]]-1);
for(int p,k,i=1;i<=q;i++){
        p=read(),k=read();
        LL ans=query(rt[id[p].first],rt[id[p].second],1,n,dep[p]+1,dep[p]+k);
        ans+=(LL)min(k,dep[p]-1)*(sz[p]-1);
        printf("%lld\n",ans);
    }
}