Submission #877113

#	Time	Username	Problem	Language	Result	Execution time	Memory
877113		AMnu	Boat (APIO16_boat)	C++14	9 / 100	2028 ms	6768 KiB

boat

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

const int MAXN = 5e2+5, MOD = 1e9+7;

int N, M, A[MAXN], B[MAXN], S[2*MAXN];
long long dp[2*MAXN][MAXN], pref[2*MAXN][MAXN], inv[MAXN];

long long comb(int x,int y) {
    long long ret = inv[y];
    for (int i=0; i<y; i++) {
        ret = ret*(x-i)%MOD;
    }
    return ret;
}

int main() {
	cin >> N;
    for (int i=1; i<=N; i++) {
        cin >> A[i] >> B[i];
        S[2*i-2] = A[i];
        S[2*i-1] = B[i]+1;
    }
    sort(S,S+2*N);
    for (int i=1; i<2*N; i++) {
        if (S[i] != S[M]) {
            M++;
            S[M] = S[i];
        }
    }
    inv[1] = 1;
    for (int i=2; i<=N; i++) {
        inv[i] = MOD - inv[N%i]*(N/i)%MOD;
    }
    for (int i=2; i<=N; i++) {
        inv[i] = inv[i-1]*inv[i]%MOD;
    }
    dp[0][0] = 1;
    for (int i=0; i<=N; i++) {
        pref[0][i] = 1;
    }
    for (int i=1; i<=M; i++) {
        pref[i][0] = 1;
        for (int j=1; j<=N; j++) {
            if (A[j]<=S[i-1] && S[i]-1<=B[j]) {
                dp[i][j] = comb(S[i]-S[i-1],1)*pref[i-1][j-1]%MOD;
                int cnt = 0;
                for (int k=j-1; k>=1; k--) {
                    if (A[k]<=S[i-1] && S[i]<=B[k]) {
                        for (int l=0; l<=cnt; l++) {
                            dp[i][j] += comb(S[i]-S[i-1],l+2)*comb(cnt,l)%MOD * dp[i-1][k-1];
                            dp[i][j] %= MOD;
                        }
                        cnt++;
                    }
                }
            }
            pref[i][j] = (dp[i][j] + pref[i][j-1] + pref[i-1][j] + MOD-pref[i-1][j-1]) % MOD;
        }
    }
    cout << (pref[M][N]+MOD-1) % MOD << '\n';
}

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