Submission #412904

#	Time	Username	Problem	Language	Result	Execution time	Memory
412904		Pbezz	Fancy Fence (CEOI20_fancyfence)	C++14	100 / 100	37 ms	7000 KiB

fancyfence

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>

using namespace std;
using namespace __gnu_pbds;
 
#define ll long long
#define pb push_back
#define mp make_pair
typedef pair<ll,ll> pii;
 
typedef tree<ll ,null_type, less<ll>, rb_tree_tag, tree_order_statistics_node_update> indexed_set;
 
const ll MAXN = 450;
const ll MOD = 1e9+7;
const ll INF = 1e9+10;
 
ll calc(ll n, ll m){
m%=MOD; n%=MOD;

ll res = (n%MOD*(n+1)%MOD)%MOD;
if(res%2==1)res+=MOD;
res/=2;
res%=MOD;

ll k = (m%MOD*(m+1)%MOD)%MOD;
if(k%2==1)k+=MOD;
k/=2;
k%=MOD;

res*=k;
res%=MOD;
if(res<0)res+=MOD;

return res;
}



int main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);

	ll n,i,k,ans=0;
	cin>>n;

	ll h[n+2],w[n+2],dp[n+2]; dp[0]=0;
	for(i=1;i<=n;i++)cin>>h[i];

	for(i=1;i<=n;i++){
	cin>>w[i];
	dp[i] = dp[i-1]+w[i];
	}

	stack <ll>st;
	ll left[n+1],right[n+1];
	bool meh[n+1];

	for(i=1;i<=n;i++){
	meh[i]=true;
	while(!st.empty()&&h[st.top()]>=h[i]){
	if(h[st.top()]==h[i])meh[i]=false;

	st.pop();
	}

	if(!st.empty()){
	left[i]=st.top();
	}else{
	left[i]=0;
	}
	st.push(i);
//cout<<left[i]<<" ";
}//cout<<endl;
while(!st.empty())st.pop();

	for(i=n;i>=1;i--){
	while(!st.empty()&&h[st.top()]>=h[i]){
	st.pop();
	}

	if(!st.empty()){
	right[i]=st.top();
	}else{
	right[i]=n+1;
	}
	st.push(i);
}

	h[0]=0;
	h[n+1]=0;
	for(i=1;i<=n;i++){

	if(meh[i]==false)continue;

	//k é a soma no intervalo
	k = dp[right[i]-1] - dp[left[i]];
	ans += calc(k,h[i]);
	ans -= calc(k , max(h[left[i]], h[right[i]]) );
	//cout<<i<<" "<<k<<" "<<h[i]<<" "<<left[i]<<" "<<right[i];
	//cout<<" "<<h[left[i]]<<" "<<h[right[i]]<<endl;
	ans%=MOD;
}


/*
6
1 2 3 2 2 1
1 1 1 1 1 1
*/

	if(ans<0)ans+=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