Submission #1235043

#	Time	Username	Problem	Language	Result	Execution time	Memory
1235043		countless	Boat (APIO16_boat)	C++20	100 / 100	466 ms	4404 KiB

boat

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef long double ld;

#define sp <<" "<<
#define endl "\n"

const ll MOD = 1e9+7;
const int MAXK = 1e3+5;

vector<int> feli;
ll inv[MAXK];

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

int o(int x) {
    return lower_bound(feli.begin(), feli.end(), x) - feli.begin();
}

void gen() {
    inv[0] = 0;

    for (int i = 1; i < MAXK; i++) {
        inv[i] = binpow(i, MOD-2);
    }
}

void solve() {
    int n; cin >> n;
    vector<int> l(n+1), r(n+1);
    for (int i = 1; i <= n; i++) {
        cin >> l[i] >> r[i];
        feli.push_back(--l[i]);
        feli.push_back(r[i]);
    }

    sort(feli.begin(), feli.end());
    feli.erase(unique(feli.begin(), feli.end()), feli.end());

    for (int i = 1; i <= n; i++) {
        l[i] = o(l[i]);
        r[i] = o(r[i]);
    }

    int m = feli.size();
    vector<vector<ll>> dp(n+1, vector<ll>(m, 0));

    dp[0][0] = 1;
    for (int j = 1; j < m; j++) {
        dp[0][j] = 1;

        for (int i = 1; i <= n; i++) {
            dp[i][j] = dp[i][j-1];
            ll cnt = 1, eff = feli[j] - feli[j-1];

            if (!(l[i] < j and j <= r[i])) continue;

            for (int k = i-1; k >= 0; k--) {
                dp[i][j] = (dp[i][j] + ((dp[k][j-1] * eff) % MOD)) % MOD;
                if (l[k] < j and j <= r[k]) {
                    eff = (((eff * (cnt + feli[j] - feli[j-1])) % MOD) * inv[cnt+1]) % MOD;
                    cnt++;
                }
            }
        }
    }

    ll ans = 0;
    for (int i = 1; i <= n; i++) ans = (ans + dp[i][m-1]) % MOD;
    cout << ans << endl;
}

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

    gen();

    int t = 1;
    // cin >> t;
    while (t--)
        solve();
}

• Subtask 1: 9 / 9
• Subtask 2: 22 / 22
• Subtask 3: 27 / 27
• Subtask 4: 42 / 42