Submission #851287

#	Time	Username	Problem	Language	Result	Execution time	Memory
851287		Jawad_Akbar_JJ	Fancy Fence (CEOI20_fancyfence)	C++14	12 / 100	3 ms	2492 KiB

fancyfence

#include <bits/stdc++.h>
 
using namespace std;
#define int long long
const int N = 1e5 + 10;
int r[N][3];
int w[N];
int h[N];
int pre[N];
int ans = 0;
int mod = 1e9 + 7;
 
int power(int a,int b){
	if (b==0)
		return 1;
	int ans = power(a,b/2);
	ans = ans*ans;
	ans %= mod;
	if (b%2)
		ans = ans*a;
	return ans%mod;
}
 
int mod_inv(int k){
	return power(k,mod-2);
}
 
int asd(int a){
	int ans = (a*(a+1));
	ans = ans%mod;
	ans = ans*mod_inv(2);
	ans = ans% mod;
	return ans;
}

int answer(int W,int H){
	int ans = asd(W);
	int ans2 = asd(H);
	return (ans*ans2)%mod ;
}

int MIN(int l,int r){
	int ind = l;
	for (int i=l;i<=r;i++)
		if (h[i]<h[ind])
			ind = i;
	return ind;
}


void solve(int l,int r,int height){
	if (r<l or l>r)
		return;
	int ind = MIN(l,r);
	int width = pre[r]-pre[l-1];
	if (width<0)
		width += mod;
	ans -= answer(width,height);
	if (ans<0)
		ans += mod;
	ans += answer(width,h[ind]);
	ans %= mod;
	solve(l,ind-1,h[ind]);
	solve(ind+1,r,h[ind]);
}

signed main(){
	int n;
	cin>>n;
	for (int i=1;i<=n;i++)
		cin>>h[i];
	int W = 0;
	for (int i=1;i<=n;i++){
		cin>>w[i];
		pre[i] = pre[i-1] + w[i];
	}
	solve(1LL,n,0LL);

	cout<<ans<<endl;

}

Compilation message (stderr)

fancyfence.cpp: In function 'int main()':
fancyfence.cpp:72:6: warning: unused variable 'W' [-Wunused-variable]
   72 |  int W = 0;
      |      ^

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