#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
const ll MOD = 1e9 + 7;
int n, cs, cf;
ll dp[2005][2005];
ll solve(int i, int k) {
if (k < 0) return 0ll;
if (i > n) return k == 1;
if (dp[i][k] != -1) return dp[i][k];
ll& ans = dp[i][k];
ans = 0;
if (i == cs || i == cf) {
ll op1 = solve(i + 1, k);
ll op2 = solve(i + 1, k + 1);
return ans = (op1 + op2) % MOD;
}
if (i < cs) {
ll op1 = (1ll * (k - 1) * solve(i + 1, k - 1)) % MOD;
ll op2 = (1ll * (k + 1) * solve(i + 1, k + 1)) % MOD;
return ans = (op1 + op2) % MOD;
}
if (i < cf) {
ll op1 = (1ll * (k - 1) * solve(i + 1, k - 1)) % MOD;
ll op2 = (1ll * k * solve(i + 1, k + 1)) % MOD;
return ans = (op1 + op2) % MOD;
}
ll op1 = (1ll * (k - 1) * solve(i + 1, k - 1)) % MOD;
ll op2 = (1ll * (k - 1) * solve(i + 1, k + 1)) % MOD;
return ans = (op1 + op2) % MOD;
}
int main(){
ios::sync_with_stdio(false);
cin.tie(0);
cin >> n >> cs >> cf;
if (cs > cf) swap(cs, cf);
memset(dp, -1, sizeof dp);
cout << solve(1, 0) << '\n';
return 0;
}
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 2 |
Correct |
18 ms |
31852 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 2 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 3 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 4 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 5 |
Correct |
21 ms |
31852 KB |
Output is correct |
| 6 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 7 |
Correct |
21 ms |
31852 KB |
Output is correct |
| 8 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 9 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 10 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 11 |
Correct |
19 ms |
31852 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 2 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 3 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 4 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 5 |
Correct |
21 ms |
31852 KB |
Output is correct |
| 6 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 7 |
Correct |
21 ms |
31852 KB |
Output is correct |
| 8 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 9 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 10 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 11 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 12 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 13 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 14 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 15 |
Correct |
22 ms |
32000 KB |
Output is correct |
| 16 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 17 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 18 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 19 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 20 |
Correct |
19 ms |
31852 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 2 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 3 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 4 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 5 |
Correct |
21 ms |
31852 KB |
Output is correct |
| 6 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 7 |
Correct |
21 ms |
31852 KB |
Output is correct |
| 8 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 9 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 10 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 11 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 12 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 13 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 14 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 15 |
Correct |
22 ms |
32000 KB |
Output is correct |
| 16 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 17 |
Correct |
18 ms |
31852 KB |
Output is correct |
| 18 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 19 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 20 |
Correct |
19 ms |
31852 KB |
Output is correct |
| 21 |
Correct |
24 ms |
31852 KB |
Output is correct |
| 22 |
Correct |
24 ms |
31980 KB |
Output is correct |
| 23 |
Correct |
25 ms |
31852 KB |
Output is correct |
| 24 |
Correct |
74 ms |
32012 KB |
Output is correct |
| 25 |
Correct |
68 ms |
31980 KB |
Output is correct |
| 26 |
Correct |
72 ms |
31980 KB |
Output is correct |
| 27 |
Correct |
76 ms |
31980 KB |
Output is correct |
| 28 |
Correct |
45 ms |
31852 KB |
Output is correct |
