Submission #85390

#	Time	Username	Problem	Language	Result	Execution time	Memory
85390		popovicirobert	Boat (APIO16_boat)	C++14	9 / 100	21 ms	2972 KiB

boat

#include <bits/stdc++.h>
#define lsb(x) (x & (-x))
#define ll long long

using namespace std;

const int MOD = (int) 1e9 + 7;
const int MAXN = 500;

inline int lgput(int a, int b) {
    int ans = 1;
    while(b > 0) {
        if(b & 1)
            ans = (1LL * ans * a) % MOD;
        b >>= 1;
        a = (1LL * a * a) % MOD;
    }
    return ans;
}

inline void mod(int &x) {
    if(x >= MOD)
        x -= MOD;
}

int dp[MAXN + 1][2 * MAXN + 1];

int main() {
    //ifstream cin("C.in");
    //ofstream cout("C.out");
    int i, j, n;
    ios::sync_with_stdio(false);
    cin >> n;
    vector <int> a(n + 1), b(n + 1);
    vector <int> nrm;
    for(i = 1; i <= n; i++) {
        cin >> a[i] >> b[i];
        b[i]++;
        nrm.push_back(a[i]);
        nrm.push_back(b[i]);
    }
    sort(nrm.begin(), nrm.end());
    nrm.resize(unique(nrm.begin(), nrm.end()) - nrm.begin());
    for(i = 1; i <= n; i++) {
        a[i] = lower_bound(nrm.begin(), nrm.end(), a[i]) - nrm.begin();
        b[i] = lower_bound(nrm.begin(), nrm.end(), b[i]) - nrm.begin();
    }
    vector <int> inv(n + 1);
    for(i = 1; i <= n; i++) {
        inv[i] = lgput(i, MOD - 2);
    }
    vector <int> len(2 * n);
    for(i = 0; i < nrm.size(); i++) {
        if(i + 1 < nrm.size()) {
            len[i] = nrm[i + 1] - nrm[i];
        }
        dp[0][i] = 1;
    }
    for(i = 1; i <= n; i++) {
        dp[i][0] = 1;
        for(j = a[i] + 1; j <= b[i]; j++) {
            dp[i][j] = (1LL * dp[i - 1][j - 1] * len[j - 1]) % MOD;
            int coef = len[j - 1];
            int nr = 1;
            for(int p = i - 2; p >= 0; p--) {
                if(a[p + 1] < j && j <= b[p + 1]) {
                    nr++;
                    if(nr > len[j - 1]) {
                        break;
                    }
                    // comb(len + nr - 2, nr)
                    coef = (1LL * coef * (len[j - 1] + nr - 2)) % MOD;
                    coef = (1LL * coef * inv[nr]) % MOD;
                    dp[i][j] = (dp[i][j] + 1LL * coef * dp[p][j - 1]) % MOD;
                }
            }
        }
        for(j = 1; j < nrm.size(); j++) {
            dp[i][j] = (1LL * dp[i][j] + dp[i - 1][j] + dp[i][j - 1] - dp[i - 1][j - 1] + MOD) % MOD;
        }
    }
    cout << (dp[n][nrm.size() - 1] - 1 + MOD) % MOD;
    //cin.close();
    //cout.close();
    return 0;
}

Compilation message (stderr)

boat.cpp: In function 'int main()':
boat.cpp:53:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(i = 0; i < nrm.size(); i++) {
                ~~^~~~~~~~~~~~
boat.cpp:54:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         if(i + 1 < nrm.size()) {
            ~~~~~~^~~~~~~~~~~~
boat.cpp:78:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(j = 1; j < nrm.size(); j++) {
                    ~~^~~~~~~~~~~~

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