Submission #556557

#	Time	Username	Problem	Language	Result	Execution time	Memory
556557		InternetPerson10	Boat (APIO16_boat)	C++17	0 / 100	438 ms	6276 KiB

boat

#include <bits/stdc++.h>
typedef long long ll;

using namespace std;

const ll MOD = 1e9 + 7;

ll modpow(ll n, ll e) {
    if(e == 0) return 1;
    ll x = modpow(n, e/2);
    x *= x; x %= MOD;
    if(e%2) {
        x *= n;
        x %= MOD;
    }
    return x;
}

ll modinv(ll n) {
    return modpow(n, MOD - 2);
}

ll smallinv[2001];

ll binom(ll n, ll k) { // Assumes k is quite small
    if(k > n) return 0;
    if(k == n) return 1;
    ll ans = 1;
    for(ll i = n-k+1; i <= n; i++) {
        ans *= i;
        ans %= MOD;
    }
    for(ll i = 1; i <= k; i++) {
        ans *= modinv(i);
        ans %= MOD;
    }
    return ans;
}

void precalc() {
    smallinv[0] = 1;
    for(int i = 1; i <= 2000; i++) {
        smallinv[i] = (smallinv[i-1] * i) % MOD;
    }
    for(int i = 0; i <= 2000; i++) {
        smallinv[i] = modinv(smallinv[i]);
    }
}

ll ans[501][1001], pref[501][1001];

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    precalc();
    int n;
    cin >> n;
    vector<int> nums(2 * n), a(n+1), b(n+1);
    for(int i = 1; i <= n; i++) {
        cin >> a[i] >> b[i];
        b[i]++;
        nums[2*i - 2] = a[i];
        nums[2*i - 1] = b[i];
    }
    sort(nums.begin(), nums.end());
    nums.resize(unique(nums.begin(), nums.end()) - nums.begin());
    for(int i = 1; i <= n; i++) {
        for(int j = 1; j < nums.size(); j++) {
            if(!(a[i] <= nums[j-1] && nums[j] <= b[i])) {
                pref[i][j] = ans[i][j] + pref[i][j-1] + pref[i-1][j] - pref[i-1][j-1];
                pref[i][j] += MOD;
                pref[i][j] %= MOD;
                continue;
            }
            ll siz = nums[j] - nums[j-1];
            ans[i][j] = siz;
            ans[i][j] += siz * pref[i-1][j-1];
            ans[i][j] %= MOD;
            int g = 1;
            for(int k = i-1; k > 0; k--) {
                if(a[k] <= nums[j-1] && nums[j] <= b[k]) {
                    g++;
                    ans[i][j] += (binom(siz+1, g) - (siz+1) + MOD) * (1 + pref[k-1][j-1]);
                    ans[i][j] %= MOD;
                }
            }
            pref[i][j] = ans[i][j] + pref[i][j-1] + pref[i-1][j] - pref[i-1][j-1];
            pref[i][j] += MOD;
            pref[i][j] %= MOD;
        }
    }
    cout << pref[n][nums.size()-1] << endl;
}

Compilation message (stderr)

boat.cpp: In function 'int main()':
boat.cpp:68:26: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   68 |         for(int j = 1; j < nums.size(); j++) {
      |                        ~~^~~~~~~~~~~~~

• Subtask 1: 0 / 9
• Subtask 2: 0 / 22
• Subtask 3: 0 / 27
• Subtask 4: 0 / 42