Submission #827540

#	Time	Username	Problem	Language	Result	Execution time	Memory
827540		PagodePaiva	Fancy Fence (CEOI20_fancyfence)	C++17	100 / 100	262 ms	8992 KiB

fancyfence

#include<bits/stdc++.h>
#define pii pair <int, int>
#define fr first
#define sc second
#define N 100010
#define inf 1e18
#define int long long

using namespace std;

int n;
int h[N], w[N];
int pref[N];
int mod = 1e9+7;

struct Segtree{
    pair <int,int> tree[4*N];

    pair <int,int> join(pii a, pii b){
        if(a.fr < b.fr) return a;
        if(a.fr > b.fr) return b;
        if(a.sc < b.sc) return a;
        return b;
    }

    void build(int l, int r, int node){
        if(l == r){
            tree[node] = {h[l], l};
            return;
        }

        int mid = (l+r)/2;

        build(l, mid, 2*node);
        build(mid+1, r, 2*node+1);

        tree[node] = join(tree[2*node], tree[2*node+1]);

        return;
    }

    pair <int, int> query(int l, int r, int tl, int tr, int node){
        if(tl > r or tr < l) return {inf, inf};
        if(l <= tl and tr <= r) return tree[node];

        int mid = (tl+tr)/2;

        return join(query(l, r, tl, mid, 2*node), query(l, r, mid+1, tr, 2*node+1));
    }
} seg;

long long binpow(long long a, long long b, long long m) {
    a %= m;
    long long res = 1;
    while (b > 0) {
        if (b & (1ll))
            res = res * a % m;
        a = a * a % m;
        b >>= (1ll);
    }
    return res;
}

int query(int l, int r, int minant){
    int c = pref[r] - pref[l-1];
    c %= mod;
    c += mod;
    c %= mod;
    int a = seg.query(l, r, 1, n, 1).fr;
    a %= mod;

    int res = (c-1)*(a-1);
    res %= mod;
    res *= c;
    res %= mod;
    res *= a;
    res %= mod;
    res *= binpow(4, mod-2, mod);
    res %= mod;
    int aux = (a+c-2)*a;
    aux %= mod;
    aux *= c;
    aux %= mod;
    aux *= binpow(2, mod-2, mod);
    aux %= mod;
    res += aux;
    res %= mod; 
    res += ((a*c) % mod);
    res %= mod;

    a = minant % mod;    

    int res2 = (c-1)*(a-1);
    res2 %= mod;
    res2 *= c;
    res2 %= mod;
    res2 *= a;
    res2 %= mod;
    res2 *= binpow(4, mod-2, mod);
    res2 %= mod;
    aux = (a+c-2)*a;
    aux %= mod;
    aux *= c;
    aux %= mod;
    aux *= binpow(2, mod-2, mod);
    aux %= mod;
    res2 += aux;
    res2 %= mod; 
    res2 += ((a*c) % mod);
    res2 %= mod;
    
    // cout << res2 << "\n";

    res = res-res2;

    res %= mod;
    res += mod;
    res %= mod;

    // cout << l << ' ' << r << ' ' << minant << ": " <<  res << "\n";

    return res % mod;
}

int32_t main(){
    cin >> n;

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

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

    seg.build(1, n, 1);

    queue <array <int,4>> q;
    q.push({1, n, 0, 0});

    for(int i = 1;i <= n;i++){
        pref[i] = pref[i-1] + w[i];
        pref[i] %= mod;
    }

    int res = 0;

    while(!q.empty()){
        auto [l, r, minant, aux] = q.front();
        q.pop();

        if(aux == 0){
            res += query(l, r, minant); res %= mod;
            auto [minn, pos] = seg.query(l, r, 1, n, 1);

            if(pos != l) q.push({l, pos-1, minn, 0});
            if(pos != r) q.push({pos+1, r, minn, 1});
        }

        else{
            auto [minn, pos] = seg.query(l, r, 1, n, 1);
            if(minant == minn){
                if(pos != l) q.push({l, pos-1, minn, 0});
                if(pos != r) q.push({pos+1, r, minn, 1});       
            }
            else{
                q.push({l, r, minant, 0});
            }
        }
    }

    // cout << binpow(4, mod-1, mod); 

    cout << res << '\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