제출 #573301

#제출 시각아이디문제언어결과실행 시간메모리
573301vladislav11Calvinball championship (CEOI15_teams)C++14
10 / 100
38 ms65536 KiB
#include <bits/stdc++.h>

using namespace std;

using ll = long long;
const ll MOD = 1e9 + 7;

int n;
vector<int> a;
vector< vector<ll> > dp;

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

    cin >> n;

    a.resize( n );

    for ( auto& el : a )
        cin >> el;

    dp.assign( n+1, vector<ll>( n+1, 0 ) );

    for ( int i=1; i<=n; i++ )
        dp[0][i] = 1;

    for ( int i=1; i<=n; i++ )
    for ( int j=1; j<=n; j++ )
    {
        if ( j+1 <= n )
            dp[i][j] = ( j*dp[i-1][j] + dp[i-1][j+1] ) % MOD;
        else
            dp[i][j] = j*dp[i-1][j] % MOD;
    }

    ll ans = 1;

    int maxi = 0;

    for ( int i=0; i<n; i++ )
    {
        for ( int j=1; j<a[i]; j++ )
            ans += dp[n-i-1][ max(maxi,j) ];

        ans %= MOD;
    }

    cout << ans;

    return 0;
}
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