Submission #334548

#TimeUsernameProblemLanguageResultExecution timeMemory
334548mehrdad_sohrabiCalvinball championship (CEOI15_teams)C++14
80 / 100
1097 ms748 KiB
#include <bits/stdc++.h>
typedef long long int ll;
typedef long double ld;
#define pb push_back
#define pii pair < ll , ll >
#define F first
#define S second
#define endl '\n'
#define int long long
#define sync ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math")
#define kill(x) return cout<<x<<'\n', 0;
using namespace std;
const int N=1e4+100;
ll dp[2][N];
ll a[N];
ll mod=1e6+7;
ll par[N];
int32_t main(){
    sync;
    ll n;
    cin >> n;
    for (int i=1;i<=n;i++){
        cin >> a[i];
    }
    for (int i=1;i<=n;i++){
        par[i]=max(par[i-1],a[i]);
    }
    for (int i=0;i<=n;i++){
        dp[0][i]=1;
    }
    ll ans=a[n];
    for (int i=1;i<n;i++){
        for (int j=1;j<=n;j++){
            dp[i%2][j]=dp[(i-1)%2][j]*j%mod+dp[(i-1)%2][j+1];
            dp[i%2][j]%=mod;
            //cout << i << " " << j << " " << dp[i][par] << endl;
        }
            ans+=dp[i%2][par[n-i-1]]*(a[n-i]-1)%mod;
    }
    cout << ans%mod;


}
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