This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
#define MASK(i) (1LL << (i))
#define GETBIT(mask, i) (((mask) >> (i)) & 1)
#define ALL(v) (v).begin(), (v).end()
#define block_of_code if(true)
ll max(ll a, ll b){return (a > b) ? a : b;}
ll min(ll a, ll b){return (a < b) ? a : b;}
ll gcd(ll a, ll b){return __gcd(a, b);}
ll lcm(ll a, ll b){return a / gcd(a, b) * b;}
ll LASTBIT(ll mask){return (mask) & (-mask);}
int pop_cnt(ll mask){return __builtin_popcountll(mask);}
int ctz(ull mask){return __builtin_ctzll(mask);}
int logOf(ull mask){return 63 - __builtin_clzll(mask);}
mt19937_64 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
ll rngesus(ll l, ll r){return l + (ull) rng() % (r - l + 1);}
double rngesus_d(double l, double r){
double cur = rngesus(0, MASK(60) - 1);
cur /= MASK(60) - 1;
return l + cur * (r - l);
}
template <class T1, class T2>
bool maximize(T1 &a, T2 b){
if (a < b) {a = b; return true;}
return false;
}
template <class T1, class T2>
bool minimize(T1 &a, T2 b){
if (a > b) {a = b; return true;}
return false;
}
template <class T>
void printArr(T container, string separator = " ", string finish = "\n", ostream &out = cout){
for(auto item: container) out << item << separator;
out << finish;
}
template <class T>
void remove_dup(vector<T> &a){
sort(ALL(a));
a.resize(unique(ALL(a)) - a.begin());
}
const int N = 1e3 + 69;
int n;
const int MOD = 1e9 + 7;
void add(int &a, int b){
a += b;
if (a >= MOD) a -= b;
}
int dp[2][N];
int main(void){
ios::sync_with_stdio(0);cin.tie(0); cout.tie(0);
clock_t start = clock();
cin >> n;
vector<int> a(n);
for(int i =0; i<n; ++i) cin >> a[i];
vector<int> pref_max = a;
for(int i = 1; i<n; ++i) maximize(pref_max[i], pref_max[i-1]);
for(int i = 1; i <= n; ++i) dp[0][i] = 1;
int ans = 1;
for(int i = n-1; i>=1; --i){
ans = (ans + 1LL * (a[i] - 1) * dp[0][pref_max[i-1]]) % MOD;
for(int j = 1; j <= i; ++j) {
dp[1][j] = dp[0][j+1];
dp[1][j] = (dp[1][j] + 1LL * dp[0][j] * j) % MOD;
}
for(int j = 1; j<=n; ++j) {
dp[0][j] = dp[1][j];
dp[1][j] = 0;
}
}
cout << ans << "\n";
cerr << "Time elapsed: " << clock() - start << " ms\n";
return 0;
}
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