#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define fi first
#define se second
#define ll long long
#define ld long double
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define pb push_back
#define mpp make_pair
#define ve vector
using namespace std;
using namespace __gnu_pbds;
template<class T> using oset = tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
const ll inf = 1e18; const int iinf = 1e9;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
template <typename T> inline bool chmin(T& a, T b) { return (a > b ? a = b, 1 : 0); }
template <typename T> inline bool chmax(T& a, T b) { return (a < b ? a = b, 1 : 0); }
const int md = 1e9 + 7;
inline int add(int a, int b) { a += b; if (a >= md){a -= md;} return a; }
inline int mul(int a, int b) { return (ll)a * b % md; }
inline void solve() {
int n, s, t;
cin >> n >> s >> t;
ve<ve<int>> dp(n + 5, ve<int> (n + 5));
dp[1][1] = 1;
for (int i = 1; i < n; ++i) {
for (int j = 1; j <= i; ++j) {
if (i + 1 == s || i + 1 == t) {
dp[i + 1][j] = add(dp[i + 1][j], dp[i][j]);
dp[i + 1][j + 1] = add(dp[i + 1][j + 1], dp[i][j]);
}
else {
int ways = j + 1 - (i + 1 > s) - (i + 1 > t);
dp[i + 1][j + 1] = add(dp[i + 1][j + 1], mul(ways, dp[i][j]));
dp[i + 1][j - 1] = add(dp[i + 1][j], mul(dp[i][j], j - 1));
}
}
}
cout << dp[n][1];
}
signed main() {
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
int q = 1; // cin >> q;
while (q--) solve();
cerr << fixed << setprecision(3) << "Time execution: " << (double)clock() / CLOCKS_PER_SEC << endl;
}
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
1 ms |
212 KB |
Output is correct |
| 2 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
1 ms |
212 KB |
Output is correct |
| 2 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
1 ms |
212 KB |
Output is correct |
| 2 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
1 ms |
212 KB |
Output is correct |
| 2 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| 3 |
Halted |
0 ms |
0 KB |
- |
