제출 #856609

#제출 시각아이디문제언어결과실행 시간메모리
856609NeroZeinCalvinball championship (CEOI15_teams)C++17
100 / 100
95 ms604 KiB
#include "bits/stdc++.h"
using namespace std;

#ifdef Nero
#include "Deb.h"
#else
#define deb(...)
#endif

const int md = 1000007;

int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int n;
  cin >> n;
  vector<int> a(n);
  vector<int> till(n); 
  for (int i = 0; i < n; ++i) {
    cin >> a[i]; 
  }
  for (int i = 1; i < n; ++i) {
    till[i] = max(till[i - 1], a[i - 1]); 
  }
  vector<int> dp(n + 1), pd(n + 1); 
  for (int i = 1; i <= n; ++i) {
    pd[i] = 1; 
  }
  int ans = 1; 
  for (int i = n - 1; i >= 0; --i) {
    ans += ((long long) pd[till[i]] * (a[i] - 1)) % md; 
    if (ans >= md) {
      ans -= md; 
    }
    for (int j = 1; j < i; ++j) {
      dp[j] = ((long long) pd[j] * j + pd[j + 1]) % md;
    }
    swap(dp, pd); 
  }
  cout << ans << '\n'; 
  return 0;
}
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