Submission #546301

#TimeUsernameProblemLanguageResultExecution timeMemory
546301Soumya1Calvinball championship (CEOI15_teams)C++17
100 / 100
251 ms468 KiB
#include <bits/stdc++.h>
#ifdef __LOCAL__
#include <debug_local.h>
#endif
using namespace std;
const int mod = 1e6 + 7;
void testCase() {
  int n;
  cin >> n;
  vector<int> a(n + 1);
  for (int i = 1; i <= n; i++) cin >> a[i];
  vector<int> dp(n + 1, 1);
  vector<int> pre(n + 1);
  for (int i = 1; i <= n; i++) pre[i] = max(pre[i - 1], a[i]);
  int ans = 0;
  for (int i = n - 1; i >= 1; i--) {
    vector<int> new_dp(n + 1);
    for (int j = 1; j <= n; j++) {
      new_dp[j] = (1LL * dp[j] * j + (j + 1 <= n ? dp[j + 1] : 0)) % mod;
    }
    ans += new_dp[pre[i]];
    if (ans >= mod) ans -= mod;
    for (int j = a[i + 1]; j <= pre[i] + 1; j++) {
      ans -= dp[max(j, pre[i])];
      if (ans < 0) ans += mod;
    }
    dp = new_dp;
  }
  cout << (ans + 1) % mod << "\n";
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  testCase();
  return 0;
}
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