BZOJ4889 & 洛谷3759：[TJOI2017]不勤劳的图书管理员——题解

#include<cmath>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
typedef long long ll;
const int N=5e4+5;
const int p=1e9+7;
inline int read(){
    int X=0,w=0;char ch=0;
    while(ch<‘0‘||ch>‘9‘){w|=ch==‘-‘;ch=getchar();}
    while(ch>=‘0‘&&ch<=‘9‘)X=(X<<3)+(X<<1)+(ch^48),ch=getchar();
    return w?-X:X;
}
struct tree{
    int l,r;
    ll v,c;
}tr[N*200];
int rt[N],pool,n,m;
ll ans,a[N],v[N],b[N],cnt[N];
inline int lowbit(int x){return x&(-x);}
inline void add(int x,int y){
    for(int i=x;i<=n;i+=lowbit(i))b[i]+=y,cnt[i]++;
}
inline ll qry_val(int x){
    ll res=0;
    for(int i=x;i;i-=lowbit(i))res+=b[i];
    return res;
}
inline ll qry_cnt(int x){
    ll res=0;
    for(int i=x;i;i-=lowbit(i))res+=cnt[i];
    return res;
}
inline void insert(int &x,int l,int r,int pos,int v,int w){
    if(!x)x=++pool;
    tr[x].v+=v;tr[x].c+=w;
    if(l==r)return;
    int mid=(l+r)>>1;
    if(pos<=mid)insert(tr[x].l,l,mid,pos,v,w);
    else insert(tr[x].r,mid+1,r,pos,v,w);
}
inline void ins(int i,int x,int y,int w){
    for(;i<=n;i+=lowbit(i))insert(rt[i],1,n,x,y,w);
}
inline ll sqv(int x,int l,int r,int l1,int r1){
    if(r<l1||r1<l)return 0;
    if(l1<=l&&r<=r1)return tr[x].v;
    int mid=(l+r)>>1;
    return sqv(tr[x].l,l,mid,l1,r1)+sqv(tr[x].r,mid+1,r,l1,r1);
}
inline ll sqc(int x,int l,int r,int l1,int r1){
    if(r<l1||r1<l)return 0;
    if(l1<=l&&r<=r1)return tr[x].c;
    int mid=(l+r)>>1;
    return sqc(tr[x].l,l,mid,l1,r1)+sqc(tr[x].r,mid+1,r,l1,r1);
}
inline ll query_val(int l,int r,int l1,int r1){
    if(l>r||l1>r1)return 0;
    l--;ll res=0;
    for(int i=r;i;i-=lowbit(i))res=(res+sqv(rt[i],1,n,l1,r1))%p;
    for(int i=l;i;i-=lowbit(i))res=(res-sqv(rt[i],1,n,l1,r1))%p;
    return (res+p)%p;
}
inline ll query_cnt(int l,int r,int l1,int r1){
    if(l>r||l1>r1)return 0;
    l--;ll res=0;
    for(int i=r;i;i-=lowbit(i))res=(res+sqc(rt[i],1,n,l1,r1))%p;
    for(int i=l;i;i-=lowbit(i))res=(res-sqc(rt[i],1,n,l1,r1))%p;
    return (res+p)%p;
}
inline void check(ll &x){
    while(x>=p)x-=p;
    while(x<0)x+=p;
}
int main(){
    n=read(),m=read();
    for(int i=1;i<=n;i++){
        a[i]=read(),v[i]=read();
        ins(i,a[i],v[i],1);
    }
    for(int i=n;i>=1;i--){
        add(a[i],v[i]);
        ans=(ans+qry_val(a[i]-1)+qry_cnt(a[i]-1)*v[i])%p;
    }
    for(int i=1;i<=m;i++){
        int l=read(),r=read();
        if(l==r){printf("%lld\n",ans);continue;}
        if(l>r)swap(l,r);
        ans=ans+query_val(l+1,r-1,1,a[r]-1);check(ans);
        ans=ans+query_cnt(l+1,r-1,1,a[r]-1)*v[r];check(ans);
        ans=ans-query_val(l+1,r-1,a[r]+1,n);check(ans);
        ans=ans-query_cnt(l+1,r-1,a[r]+1,n)*v[r];check(ans);
        ans=ans+query_val(l+1,r-1,a[l]+1,n);check(ans);
        ans=ans+query_cnt(l+1,r-1,a[l]+1,n)*v[l];check(ans);
        ans=ans-query_val(l+1,r-1,1,a[l]-1);check(ans);
        ans=ans-query_cnt(l+1,r-1,1,a[l]-1)*v[l];check(ans);
        if(a[l]>a[r])ans-=v[l]+v[r];
        else ans+=v[l]+v[r];
        check(ans);
        ins(l,a[l],-v[l],-1);ins(r,a[r],-v[r],-1);
        swap(a[l],a[r]);swap(v[l],v[r]);
        ins(l,a[l],v[l],1);ins(r,a[r],v[r],1);
        printf("%lld\n",ans);
    }
    return 0;
}