BZOJ 3745

#include <bits/stdc++.h>
using namespace std;
#define rint register int
#define IL inline
#define rep(i,h,t) for (rint i=h;i<=t;i++)
#define dep(i,t,h) for (rint i=t;i>=h;i--)
#define ll long long
#define mid ((h+t)>>1)
const int N=6e5;
const int mo=1e9;
int a[N],sum[N],sum2[N],sum3[N],sum4[N],sum5[N],sum6[N];
ll ans=0;
void fz(int h,int t)
{
if (h==t)
{
ans=(ans+1ll*a[h]*a[h])%mo;
return;
}
int mina=a[mid],maxa=a[mid];
sum[mid+1]=sum2[mid+1]=sum3[mid+1]=sum4[mid+1]=0;
dep(i,mid,h)
{
mina=min(a[i],mina);
maxa=max(a[i],maxa);
sum[i]=(sum[i+1]+(1ll*mina*maxa)%mo*(mid-i+1))%mo;
sum2[i]=(sum2[i+1]+1ll*mina*maxa)%mo;
sum3[i]=(sum3[i+1]+1ll*(mid-i+1)*mina)%mo;
sum4[i]=(sum4[i+1]+mina)%mo;
sum5[i]=(sum5[i+1]+1ll*(mid-i+1)*maxa)%mo;
sum6[i]=(sum6[i+1]+maxa)%mo;
}
mina=a[mid],maxa=a[mid];
int pos1=mid,pos2=mid;
rep(i,mid,t)
{
mina=min(a[i],mina);
maxa=max(a[i],maxa);
while (a[pos1]>=mina&&pos1>=h) pos1--; pos1++;
while (a[pos2]<=maxa&&pos2>=h) pos2--; pos2++;
if (pos2<pos1)
{
ans+=(1ll*(2*i-mid-pos1+2)*(mid-pos1+1)/2)%mo*mina%mo*maxa%mo;
ans+=(sum3[pos2]-sum3[pos1]+1ll*(i-mid)*(sum4[pos2]-sum4[pos1]))%mo*maxa%mo;
ans+=(sum[h]-sum[pos2]+1ll*(i-mid)*(sum2[h]-sum2[pos2]))%mo;
ans%=mo;
} else
{
ans+=(1ll*(2*i-mid-pos2+2)*(mid-pos2+1)/2)%mo*mina%mo*maxa%mo;
ans+=(sum5[pos1]-sum5[pos2]+1ll*(i-mid)*(sum6[pos1]-sum6[pos2]))%mo*mina%mo;
ans+=(sum[h]-sum[pos1]+1ll*(i-mid)*(sum2[h]-sum2[pos1]))%mo;
ans%=mo;
}
}
if (h<=mid-1) fz(h,mid-1);
if (mid+1<=t) fz(mid+1,t);
}
int main()
{
freopen("1.in","r",stdin);
freopen("1.out","w",stdout);
ios::sync_with_stdio(false);
int n;
cin>>n;
rep(i,1,n) cin>>a[i];
fz(1,n);
cout<<ans<<endl;
return 0;
}

posted @ 2018-07-08 23:13  尹吴潇  阅读(117)  评论(0编辑  收藏  举报