Submission #679651

#	Time	Username	Problem	Language	Result	Execution time	Memory
679651		bebra	Boat (APIO16_boat)	C++17	100 / 100	408 ms	4384 KiB

boat

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

#define dbg(x) cerr << #x << ": " << x << endl;

const int MOD = 1e9 + 7;

int add(int a, int b) {
    int res = a + b;
    if (res >= MOD) res -= MOD;
    return res;
}

int mul(long long a, int b) {
    return a * b % MOD;
}

int binpow(int base, int power) {
    int res = 1;
    while (power > 0) {
        if (power & 1) {
            res = mul(res, base);
        }
        base = mul(base, base);
        power >>= 1;
    }
    return res;
}

const int MAX_N = 500 + 5;
int dp[MAX_N][MAX_N * 2];
int c[MAX_N * 2][MAX_N];

int a[MAX_N];
int b[MAX_N];


int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int n;
    cin >> n;
    vector<int> p;
    for (int i = 1; i <= n; ++i) {
        cin >> a[i] >> b[i];
        p.push_back(a[i]);
        p.push_back(b[i] + 1);
    }
    sort(p.begin(), p.end());
    p.resize(unique(p.begin(), p.end()) - p.begin());
    vector<pair<int, int>> segments;
    for (int i = 0; i < (int)p.size() - 1; ++i) {
        for (int j = 1; j <= n; ++j) {
            if (a[j] <= p[i] && p[i + 1] - 1 <= b[j]) {
                segments.emplace_back(p[i], p[i + 1] - 1);
                break;
            }
        }
    }
    int m = segments.size();
    segments.insert(segments.begin(), {-1, -1});
    for (int i = 1; i <= m; ++i) {
        auto [l, r] = segments[i];
        c[i][1] = r - l + 1;
        for (int j = 2; j <= n; ++j) {
            c[i][j] = mul(c[i][j - 1], mul(r - l + j, binpow(j, MOD - 2)));
        }
    }
    for (int j = 0; j <= m; ++j) {
        dp[0][j] = 1;
    }
    for (int i = 1; i <= n; ++i) {
        dp[i][0] = 1;
        for (int j = 1; j <= m; ++j) {
            auto [l, r] = segments[j];
            dp[i][j] = dp[i][j - 1];
            int cnt = 0;
            for (int k = i; k >= 1; --k) {
                if (a[k] <= l && r <= b[k]) {
                    ++cnt;
                    dp[i][j] = add(dp[i][j], mul(dp[k - 1][j - 1], c[j][cnt]));
                }
            }
        }
    }
    cout << dp[n][m] - 1 << '\n';
    return 0;
}

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