Submission #573330

#TimeUsernameProblemLanguageResultExecution timeMemory
573330vladislav11Calvinball championship (CEOI15_teams)C++14
0 / 100
37 ms65536 KiB
#include <bits/stdc++.h>

using namespace std;

using ll = long long;
const ll MOD = 1e6 + 7;

int n;
vector<int> a;

const int N = 1e4 + 100;
ll dp[N][N];

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

    cin >> n;

    a.resize( n );

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

    for ( int i=0; i<N; i++ )
    for ( int j=0; j<N; j++ )
        dp[i][j] = 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++ )
        dp[i][j] = ( j*dp[i-1][j] + ( j<n ? dp[i-1][j+1] : 0 ) ) % MOD;

    ll ans = 1;

    int maxi = 0;

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

        maxi = max( maxi, a[i] );
    }

    cout << ans;

    return 0;
}
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