/*
Khangnh's code
“You can either experience the pain of discipline or the pain of regret.
The choice is yours.”
*/
// - Only when necessary :d
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize("unroll-loops")
// #pragma GCC target("avx,avx2,fma")
#include <bits/stdc++.h>
using namespace std;
#define fileopen(a, b) freopen(((string)a + ".inp").c_str(), "r", stdin); freopen(((string)b + ".out").c_str(), "w", stdout);
#define ll long long
// #define int long long
#define ld long double
#define fi first
#define se second
#define pb push_back
#define pf push_front
#define pob pop_back
#define pof pop_front
#define eb emplace_back
typedef pair<int, int> pii;
const ll mod = 1e9 + 7;
const ll inf = 1e9 + 7;
const double eps = 1e-9;
inline void sadd(ll &x, const ll &y) {x = (x + y)%mod;}
inline ll mmul(const ll &x, const ll &y) {return (x*y)%mod;}
int n, s, e;
ll dp[2005][2005];
// - Main idea: for a more detailed explanation, read
// +) https://codeforces.com/blog/entry/47764?#comment-704139
void solve() {
cin >> n >> s >> e;
memset(dp, 0, sizeof(dp));
dp[0][0] = 1;
for (int i = 0; i < n; ++i) {
for (int j = 0; j <= i; ++j) {
if (i + 1 == s || i + 1 == e) {
sadd(dp[i + 1][j + 1], dp[i][j]);
sadd(dp[i + 1][j], dp[i][j]);
} else {
sadd(dp[i + 1][j - 1], mmul(dp[i][j], j - 1));
sadd(dp[i + 1][j + 1], mmul(dp[i][j], j + 1 - (i + 1 > s) - (i + 1 > e)));
}
}
}
cout << dp[n][1];
}
signed main() {
#ifdef LOCAL
fileopen("input", "output");
auto start = clock();
#endif
#ifndef LOCAL
// fileopen("LAH", "LAH");
#endif
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int test = 1;
// cin >> test;
for (int tc = 1; tc <= test; ++tc) solve();
#ifdef LOCAL
auto end = clock();
cout << "\n\nExecution time : " << double(end - start)/CLOCKS_PER_SEC << "[s]";
#endif
return 0;
}
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
13 ms |
31692 KB |
Output is correct |
| 2 |
Correct |
13 ms |
31684 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
13 ms |
31692 KB |
Output is correct |
| 2 |
Correct |
13 ms |
31684 KB |
Output is correct |
| 3 |
Correct |
13 ms |
31672 KB |
Output is correct |
| 4 |
Correct |
14 ms |
31760 KB |
Output is correct |
| 5 |
Correct |
15 ms |
31672 KB |
Output is correct |
| 6 |
Correct |
14 ms |
31764 KB |
Output is correct |
| 7 |
Correct |
14 ms |
31724 KB |
Output is correct |
| 8 |
Correct |
15 ms |
31692 KB |
Output is correct |
| 9 |
Correct |
15 ms |
31664 KB |
Output is correct |
| 10 |
Correct |
14 ms |
31732 KB |
Output is correct |
| 11 |
Correct |
14 ms |
31792 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
13 ms |
31692 KB |
Output is correct |
| 2 |
Correct |
13 ms |
31684 KB |
Output is correct |
| 3 |
Correct |
13 ms |
31672 KB |
Output is correct |
| 4 |
Correct |
14 ms |
31760 KB |
Output is correct |
| 5 |
Correct |
15 ms |
31672 KB |
Output is correct |
| 6 |
Correct |
14 ms |
31764 KB |
Output is correct |
| 7 |
Correct |
14 ms |
31724 KB |
Output is correct |
| 8 |
Correct |
15 ms |
31692 KB |
Output is correct |
| 9 |
Correct |
15 ms |
31664 KB |
Output is correct |
| 10 |
Correct |
14 ms |
31732 KB |
Output is correct |
| 11 |
Correct |
14 ms |
31792 KB |
Output is correct |
| 12 |
Correct |
14 ms |
31748 KB |
Output is correct |
| 13 |
Correct |
14 ms |
31692 KB |
Output is correct |
| 14 |
Correct |
14 ms |
31728 KB |
Output is correct |
| 15 |
Correct |
15 ms |
31692 KB |
Output is correct |
| 16 |
Correct |
14 ms |
31692 KB |
Output is correct |
| 17 |
Correct |
14 ms |
31692 KB |
Output is correct |
| 18 |
Correct |
14 ms |
31732 KB |
Output is correct |
| 19 |
Correct |
15 ms |
31780 KB |
Output is correct |
| 20 |
Correct |
14 ms |
31688 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
13 ms |
31692 KB |
Output is correct |
| 2 |
Correct |
13 ms |
31684 KB |
Output is correct |
| 3 |
Correct |
13 ms |
31672 KB |
Output is correct |
| 4 |
Correct |
14 ms |
31760 KB |
Output is correct |
| 5 |
Correct |
15 ms |
31672 KB |
Output is correct |
| 6 |
Correct |
14 ms |
31764 KB |
Output is correct |
| 7 |
Correct |
14 ms |
31724 KB |
Output is correct |
| 8 |
Correct |
15 ms |
31692 KB |
Output is correct |
| 9 |
Correct |
15 ms |
31664 KB |
Output is correct |
| 10 |
Correct |
14 ms |
31732 KB |
Output is correct |
| 11 |
Correct |
14 ms |
31792 KB |
Output is correct |
| 12 |
Correct |
14 ms |
31748 KB |
Output is correct |
| 13 |
Correct |
14 ms |
31692 KB |
Output is correct |
| 14 |
Correct |
14 ms |
31728 KB |
Output is correct |
| 15 |
Correct |
15 ms |
31692 KB |
Output is correct |
| 16 |
Correct |
14 ms |
31692 KB |
Output is correct |
| 17 |
Correct |
14 ms |
31692 KB |
Output is correct |
| 18 |
Correct |
14 ms |
31732 KB |
Output is correct |
| 19 |
Correct |
15 ms |
31780 KB |
Output is correct |
| 20 |
Correct |
14 ms |
31688 KB |
Output is correct |
| 21 |
Correct |
15 ms |
31692 KB |
Output is correct |
| 22 |
Correct |
16 ms |
31692 KB |
Output is correct |
| 23 |
Correct |
16 ms |
31692 KB |
Output is correct |
| 24 |
Correct |
31 ms |
31692 KB |
Output is correct |
| 25 |
Correct |
30 ms |
31692 KB |
Output is correct |
| 26 |
Correct |
30 ms |
31692 KB |
Output is correct |
| 27 |
Correct |
30 ms |
31692 KB |
Output is correct |
| 28 |
Correct |
23 ms |
31692 KB |
Output is correct |
