Submission #756832

#	Time	Username	Problem	Language	Result	Execution time	Memory
756832		Tsovak	Fancy Fence (CEOI20_fancyfence)	C++17	100 / 100	37 ms	7316 KiB

fancyfence

// -------------------- Includes -------------------- //
#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <stdio.h>
#include <cstdlib>
#include <stdlib.h>
#include <array>
#include <string>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <math.h>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <bitset>
#include <list>
#include <iterator>
#include <numeric>
#include <complex>
#include <tuple>
#include <utility>
#include <cassert>
#include <assert.h>
#include <climits>
#include <limits.h>
#include <ctime>
#include <time.h>
#include <random>
#include <chrono>
#include <fstream>
using namespace std;

// -------------------- Typedefs -------------------- //

typedef long long ll;
typedef unsigned long long ull;
typedef double db;
typedef long double ld;

// -------------------- Defines -------------------- //

#define pr pair
#define mpr make_pair
#define ff first
#define ss second

#define mset multiset
#define mmap multimap
#define uset unordered_set
#define umap unordered_map
#define umset unordered_multiset
#define ummap unordered_multimap
#define pqueue priority_queue

#define sz(x) (int((x).size()))
#define len(x) (int((x).length()))
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define clr(x) (x).clear()

#define pf push_front
#define pb push_back
#define popf pop_front
#define popb pop_back
#define ft front
#define bk back

#define lb lower_bound
#define ub upper_bound
#define bs binary_search

// -------------------- Constants -------------------- //

const int MAX = int(1e9 + 5);
const ll MAXL = ll(1e18 + 5);
const ll MOD = ll(1e9 + 7);
const ll MOD2 = ll(998244353);

// -------------------- Functions -------------------- //

void fastio()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	return;
}

void precision(int x)
{
	cout.setf(ios::fixed | ios::showpoint);
	cout.precision(x);
	return;
}

ll gcd(ll a, ll b)
{
	while (b) {
		a %= b;
		swap(a, b);
	}
	return a;
}

ll lcm(ll a, ll b)
{
	return a / gcd(a, b) * b;
}

bool is_prime(ll a)
{
	if (a == 1) {
		return false;
	}
	for (ll i = 2; i * i <= a; i++) {
		if (a % i == 0) {
			return false;
		}
	}
	return true;
}

bool is_square(ll a)
{
	ll b = ll(sqrt(a));
	return (b * b == a);
}

bool is_cube(ll a)
{
	ll b = ll(cbrt(a));
	return (b * b * b == a);
}

int digit_sum(ll a)
{
	int sum = 0;
	while (a) {
		sum += int(a % 10);
		a /= 10;
	}
	return sum;
}

ll binpow(ll a, int b)
{
	ll ans = 1;
	while (b) {
		if ((b & 1) == 1) {
			ans *= a;
		}
		b >>= 1;
		a *= a;
	}
	return ans;
}

ll binpow_by_mod(ll a, ll b, ll mod)
{
	ll ans = 1;
	while (b) {
		if ((b & 1) == 1) {
			ans *= a;
			ans %= mod;
		}
		b >>= 1;
		a *= a;
		a %= mod;
	}
	return ans;
}

ll factorial(int a)
{
	ll ans = 1;
	for (int i = 2; i <= a; i++) {
		ans *= ll(i);
	}
	return ans;
}

ll factorial_by_mod(int a, ll mod)
{
	ll ans = 1;
	for (int i = 2; i <= a; i++) {
		ans *= ll(i);
		ans %= mod;
	}
	return ans;
}

// -------------------- Solution -------------------- //

const int N = 100005;
ll h[N], w[N], p[N];
int n;

int e[N];

ll dp[N];

void solve()
{
	int i, j;

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

	stack<pr<ll, int>> s;

	for (i = 1; i <= n; i++) {
		while (!s.empty() && s.top().ff >= h[i]) s.pop();

		if (s.empty()) e[i] = 0;
		else e[i] = s.top().ss;

		s.push(mpr(h[i], i));
	}

	ll ans = 0, c;

	for (i = 1; i <= n; i++) {
		c = (h[i] * (h[i] + 1) / 2) % MOD;
		dp[i] = (c * ((p[i - 1] - p[e[i]]) % MOD)) % MOD;
		dp[i] = (dp[i] + dp[e[i]]) % MOD;

		ans += (dp[i] * w[i]) % MOD;
		ans %= MOD;

		dp[i] += (c * w[i]) % MOD;
		dp[i] %= MOD;

		ans += (c * ((w[i] * (w[i] + 1) / 2) % MOD)) % MOD;
		ans %= MOD;
	}

	cout << ans << "\n";

	return;
}

void precalc()
{
	return;
}

int main()
{
	fastio();

	precalc();

	int tests = 1, tc;
	//cin >> tests;
	for (tc = 1; tc <= tests; tc++) {
		solve();
	}

	//cout << db(clock()) / CLOCKS_PER_SEC << endl;

	return 0;
}

/*
	# # # #   # # # #   # # # #   #       #    #       #     #
	   #      #         #     #    #     #    # #      #   #
	   #      # # # #   #     #     #   #    #   #     # #
	   #            #   #     #      # #    # # # #    #   #
	   #      # # # #   # # # #       #    #       #   #     #
*/

Compilation message (stderr)

fancyfence.cpp: In function 'void solve()':
fancyfence.cpp:213:9: warning: unused variable 'j' [-Wunused-variable]
  213 |  int i, j;
      |         ^

• 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