Submission #701504

#	Time	Username	Problem	Language	Result	Execution time	Memory
701504		PCTprobability	Fancy Fence (CEOI20_fancyfence)	C++14	100 / 100	80 ms	4920 KiB

fancyfence

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll mod = 1000000007;
#define fi first
#define se second
int main(){
  ll n;
  cin>>n;
  vector<ll> a(n),b(n);
  for(int i=0;i<n;i++) cin>>a[i];
  for(int i=0;i<n;i++) cin>>b[i];
  ll ans=0;
  for(int i=0;i<n;i++) (ans+=((b[i]*(b[i]+1))/2%mod)*((a[i]*(a[i]+1)/2)%mod))%=mod;
  ans%=mod;
  vector<pair<ll,ll>> s;
  ll sum=0;
  for(int i=0;i<n;i++){
    if(i==0){
      s.push_back({a[i],b[i]});
      sum+=(a[i]*(a[i]+1)/2)%mod*b[i];
      sum%=mod;
      continue;
    }
    ll sum2=b[i];
    while(s.size()&&s.back().fi>a[i]){
      sum2+=s.back().se;
      sum-=(s.back().fi*(s.back().fi+1)/2%mod)*s.back().se%mod;
      sum%=mod;
      sum+=mod;
      sum%=mod;
      s.pop_back();
    }
    sum2%=mod;
    ans+=sum*b[i];
    ans+=(a[i]*(a[i]+1)/2%mod)*(sum2-b[i]+mod)%mod*b[i]%mod;
    sum+=(a[i]*(a[i]+1)/2)%mod*sum2%mod;
    sum%=mod;
    ans%=mod;
    s.push_back({a[i],sum2%mod});
  }
  cout<<ans<<endl;
}

• Subtask 1: 0 / 0
• Subtask 2: 12 / 12
• Subtask 3: 13 / 13
• Subtask 4: 15 / 15
• Subtask 5: 15 / 15
• Subtask 6: 18 / 18
• Subtask 7: 27 / 27