Submission #881895

#	Time	Username	Problem	Language	Result	Execution time	Memory
881895		1L1YA	Fancy Fence (CEOI20_fancyfence)	C++17	100 / 100	22 ms	6712 KiB

fancyfence

//1L1YA
#include<bits/stdc++.h>
using namespace std;
#define ll           long long
#define Pb           push_back
#define dokme(x)     cout << x << endl, exit(0)
#define pii          pair<int,int>
#define F            first
#define S            second
#define endl         '\n'
#define sep          ' '
#define all(x)       x.begin(),x.end()
#define FastIO       ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define lc           id<<1
#define rc           lc|1

const ll mod=1e9+7;
const ll oo=4e18;
const int N=1e5+5;
const int lg=23;

ll n,in=(mod+1)/2,h[N],w[N],dp[N],lst[N],sum[N];

ll C(ll x){
    x%=mod;
    return (x*(x-1)%mod*in%mod)%mod;
}

int main(){
    FastIO

    cin >> n;
    for(int i=1;i<=n;i++)
        cin >> h[i];
    for(int i=1;i<=n;i++)
        cin >> w[i],sum[i]=(sum[i-1]+w[i])%mod;
    vector<int> st;
    st.Pb(0);
    for(int i=1;i<=n;i++){
        while(h[i]<=h[st.back()])
            st.pop_back();
        lst[i]=st.back();
        st.Pb(i);
    }
    ll ans=0;
    for(int i=1;i<=n;i++){
        ll W=(sum[i]-sum[lst[i]]+mod)%mod;
        ll p=C(W+1);
        p=(p-C((W-w[i]+1+mod)%mod)+mod)%mod;
        ans=(ans+p*C(h[i]+1)%mod)%mod;
        ans=(ans+dp[lst[i]]*w[i]%mod)%mod;
        dp[i]=(W*C(h[i]+1)%mod+dp[lst[i]])%mod;
    }
    cout << ans << endl;

    return 0;
}

• 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