#include <bits/stdc++.h>
using namespace std;
#define f first
#define s second
#define pb push_back
#define ar array
#define all(x) x.begin(), x.end()
#define siz(x) (int)x.size()
#define FOR(x, y, z) for(int x = (y); x < (z); x++)
#define ROF(x, z, y) for(int x = (y-1); x >= (z); x--)
#define F0R(x, z) FOR(x, 0, z)
#define R0F(x, z) ROF(x, 0, z)
#define trav(x, y) for(auto&x:y)
using ll = long long;
using vi = vector<int>;
using vl = vector<long long>;
using pii = pair<int, int>;
using vpii = vector<pair<int, int>>;
template<class T> inline bool ckmin(T&a, T b) {return b < a ? a = b, 1 : 0;}
template<class T> inline bool ckmax(T&a, T b) {return b > a ? a = b, 1 : 0;}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const char nl = '\n';
const int mxN = 1e4 + 10;
const int MOD = 1'000'007;
const long long infLL = 1e18;
// modulo class
int add(int x, int y){ x += y; while(x >= MOD) x -= MOD; while(x < 0) x += MOD; return x; } void ad(int &x, int y) {x = add(x, y);}
int sub(int x, int y){ x -= y; while(x >= MOD) x -= MOD; while(x < 0) x += MOD; return x; } void sb(int &x, int y) {x = sub(x, y);}
int mul(int x, int y){ return ((int64_t)x * (int64_t)y) % MOD; } void ml(int &x, int y) {x = mul(x, y);}
int binpow(int x, int y){ int z = 1; while(y > 0) { if(y % 2 == 1) z = mul(z, x); x = mul(x, x); y /= 2; } return z; }
int inv(int x){ return binpow(x, MOD - 2); }
int divide(int x, int y){ return mul(x, inv(y)); }
int n, res = 1, dp[2][mxN]; vector<int> a, b;
int32_t main(){
ios_base::sync_with_stdio(0); cin.tie(0);
cin >> n;
a.resize(n+1); b.resize(n+1);
F0R(i, n) {
cin >> a[i];
if(i)
b[i]=max(b[i-1], a[i-1]);
dp[0][i] = 1;
}
for (int i = n - 1; i>=0; i--) {
res = (res + ((a[i] - 1) * dp[0][b[i]]));
ad(res, mul((a[i]-1), dp[0][b[i]]));
FOR(j, 0, i)
dp[1][j] = mul(j * dp[0][j] , dp[0][j + 1]);
FOR(j, 0, n + 1) dp[0][j] = dp[1][j];
}
cout << res << nl;
}
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
1 ms |
384 KB |
Output is correct |
2 |
Incorrect |
1 ms |
384 KB |
Output isn't correct |
3 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
1 ms |
384 KB |
Output is correct |
2 |
Incorrect |
1 ms |
384 KB |
Output isn't correct |
3 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
1 ms |
384 KB |
Output isn't correct |
2 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
1 ms |
384 KB |
Output isn't correct |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
1 ms |
384 KB |
Output isn't correct |
2 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
1 ms |
384 KB |
Output isn't correct |
2 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
2 ms |
384 KB |
Output isn't correct |
2 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
178 ms |
588 KB |
Output isn't correct |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
44 ms |
384 KB |
Output isn't correct |
2 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
182 ms |
512 KB |
Output isn't correct |
2 |
Halted |
0 ms |
0 KB |
- |