Submission #987867

#	Time	Username	Problem	Language	Result	Execution time	Memory
987867		VMaksimoski008	Fancy Fence (CEOI20_fancyfence)	C++17	100 / 100	110 ms	9036 KiB

fancyfence

#include <bits/stdc++.h>
#define int long long
using namespace std;
using ll = long long;

const int mod = 1e9 + 7;

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%mod) - C((l-1+mod)%mod) + mod) % mod; }

struct DSU {
    int n, comp;
    vector<int> par, size, W;

    void config(int _n) {
        n = _n + 1;
        comp = _n;
        par.resize(n+1);
        size.resize(n+1, 1);
        W.resize(n+1);
        for(int i=1; i<=n; i++) par[i] = i;
    }

    int get(int u) {
        if(u == par[u]) return u;
        return par[u] = get(par[u]);
    }

    bool uni(int u, int v) {
        u = get(u), v = get(v);

        if(u == v) return 0;
        if(size[u] < size[v]) swap(u, v);

        size[u] += size[v];
        W[u] = (W[u] + W[v]) % mod;
        par[v] = u;

        return 1;
    }

    void setW(int p, int w) { W[get(p)] += w; }
    ll getW(int p) { return W[get(p)]; }
};

struct Edge {
    int a, b, w;
    bool operator<(Edge &e) { return w > e.w;}
};


int32_t main() {
    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];

    ll ans = 0;

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

    DSU dsu; dsu.config(n);
    for(int i=1; i<=n; i++) dsu.setW(i, w[i]);

    vector<Edge> edges;
    for(int i=1; i<n; i++) edges.push_back({ i, i + 1, min(h[i], h[i+1]) });
    sort(edges.begin(), edges.end());

    for(Edge &e : edges) {
        ll L = dsu.getW(e.a), R = dsu.getW(e.b);
        dsu.uni(e.a, e.b);
        ans = (ans + (R + mod) % mod * C(e.w) % mod * (L + mod) % mod) % mod;
    }

    cout << ans << '\n';
    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