Submission #610286

#	Time	Username	Problem	Language	Result	Execution time	Memory
610286		Arnch	Fancy Fence (CEOI20_fancyfence)	C++17	100 / 100	41 ms	5192 KiB

fancyfence

// oooo
/*
 har chi delet mikhad bebar ~
 gitar o ba khodet nabar! ~
 ;Amoo_Hasan;
*/

#include<bits/stdc++.h>
//#pragma GCC optimize("O3,no-stack-protector,unroll-loops")
//#pragma GCC target("avx2,fma")

using namespace std;

typedef long long ll;
typedef long double ld;

#define Sz(x) int((x).size())
#define All(x) (x).begin(), (x).end()
#define wtf(x) cout<<#x <<" : " <<x <<endl

constexpr ll inf = 1e18, N = 1e5 + 10, mod = 1e9 + 7, pr = 1000696969;

int w[N], h[N];
int l[N], r[N];
ll ps[N], bpow;

ll poww(ll x, int y) {
	ll res = 1;
	for(; y; y /= 2, x = x * x % mod)
		if(y & 1) {
			res *= x;
			res %= mod;
		}
	return res;
}

ll choose(ll x) {
	ll ans = (x * (x - 1)) % mod;
	ans *= bpow;
	ans %= mod;
	return ans;
}

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

	bpow = poww(2, mod - 2);
	
	int n; cin >>n;
	for(int i = 0; i < n; i++) cin >>h[i];
	for(int i = 0; i < n; i++) cin >>w[i];

	vector<int> vc;
	for(int i = 0; i < n; i++) {
		while(!vc.empty() && h[vc.back()] >= h[i]) vc.pop_back();
		if(vc.empty()) l[i] = 0;
		else l[i] = vc.back() + 1;
		vc.push_back(i);
	}
	vc.clear();

	for(int i = n - 1; i >= 0; i--) {
		while(!vc.empty() && h[vc.back()] > h[i]) vc.pop_back();
		if(vc.empty()) r[i] = n - 1;
		else r[i] = vc.back() - 1;
		vc.push_back(i);
	}
	for(int i = 0; i < n; i++) {
		ps[i] = w[i];
		if(i > 0) ps[i] += ps[i - 1];

		ps[i] %= mod;
	}

	ll ans = 0;
	for(int i = 0; i < n; i++) {
		int mx = 0;
		if(l[i] > 0) mx = max(mx, h[l[i] - 1] + 1);
		if(r[i] < n - 1) mx = max(mx, h[r[i] + 1] + 1);

		ll cnt = (choose(h[i] + 1) - choose(mx) + mod) % mod;
			
		ll num = ps[r[i]];
		if(l[i] > 0) num -= ps[l[i] - 1];
		if(num < 0) num += mod;
		num = choose(num + 1);

		cnt *= num, cnt %= mod;

		ans += cnt, ans %= mod;
	}
	
	cout<<ans;

    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