Submission #987842

#	Time	Username	Problem	Language	Result	Execution time	Memory
987842		VMaksimoski008	Fancy Fence (CEOI20_fancyfence)	C++17	60 / 100	296 ms	6484 KiB

fancyfence

#include <bits/stdc++.h>

#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
//#define int long long

using namespace std;

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

const int mod = 1e9 + 7;
const int LOG = 20;
const int maxn = 1e5 + 5;
const double eps = 1e-9;

ll exp(ll a, ll b) {
    ll ans = 1;
    while(b) {
        if(b & 1) ans = (ans * a) % mod;
        a = (a * a) % mod;
        b /= 2;
    }
    return ans;
}

ll inv(ll a) {
    return exp(a, mod - 2);
}

ll C(ll a) {
    return a * (a + 1) % mod * inv(2) % mod;
}

ll S(ll l, ll r) {
    return (C(r) - C(l-1) + mod) % mod;
}

int32_t main() {
    ios_base::sync_with_stdio(false);
    cout.tie(0); cin.tie(0);

    int n;
    cin >> n;
    vector<ll> h(n+1), w(n+1);
    for(int i=1; i<=n; i++) cin >> h[i];
    for(int i=1; i<=n; i++) cin >> w[i];

    set<ll> s;
    for(int i=1; i<=n; i++) s.insert(h[i]);

    if(s.size() == 1) {
        ll W = 0, H = h[1];
        for(int i=1; i<=n; i++) W = (W + w[i]) % mod;
        cout << C(W) * C(H) % mod << '\n'; 
        return 0;
    }

    bool inc = true;
    for(int i=1; i<n; i++) if(h[i] > h[i+1]) inc = false;

    if(inc) {
        ll ans = 0, W = 0;

        for(int i=n; i>=1; i--) {
            W = (W + w[i]) % mod;
            ans = (ans + S(W-w[i]+1, W) * C(h[i])) % mod;
        }

        cout << ans << '\n';
        return 0;
    }

    if(n <= 1000) {
        ll ans = 0;

        vector<ll> pref(n+1);
        for(int i=1; i<=n; i++) pref[i] = (pref[i-1] + w[i]) % mod;

        auto query = [&](int l, int r) { return ( l > r ? 0 : (pref[r] - pref[l-1] + mod) % mod ); };

        for(int i=1; i<=n; i++) {
            ll H = h[i];
            for(int j=i+1; j<=n; j++) {
                H = min(H, h[j]);
                //cout << H << " " << query(i, j) << " " << query(i, j-1) << " " << query(i+1, j) << " " << query(i+1, j-1) << '\n';
                ans = (ans + C(H) * C(query(i, j)) % mod) % mod;
                ans = (ans - C(H) * C(query(i, j-1)) + mod % mod) % mod;
                ans = (ans - C(H) * C(query(i+1, j)) + mod % mod) % mod;
                ans = (ans + C(H) * C(query(i+1, j-1)) + mod % mod) % mod;
            }
        }

        for(int i=1; i<=n; i++) ans = (ans + C(w[i]) * C(h[i])) % mod;

        cout << ans << '\n';
        return 0;
    }

    return 0;
}

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