#include <bits/stdc++.h>
#define int int64_t
using namespace std;
const int maxn = 2010;
const int mod = 1e9 + 7;
int dp[maxn][maxn];
int n;
int ini, fim;
int solve(int i, int k) {
if (i == n+1 && k == 1) return 1;
else if (i == n+1) return 0;
if (dp[i][k] != -1) return dp[i][k];
int caso1 = solve(i+1, k+1);
int caso2 = (k ? solve(i+1, k-1) : 0);
if (i == ini || i == fim) return dp[i][k] = (caso1 + caso2)%mod;
else if (i < ini && i < fim) return dp[i][k] = ( caso1*(k+1) + caso2*(k-1) )%mod;
else if (i < ini || i < fim) return dp[i][k] = ( caso1*k + caso2*(k-1) )%mod;
return dp[i][k] = ((k-1)*( caso1 + caso2 ))%mod;
}
int32_t main() {
memset(dp, -1, sizeof dp);
cin >> n;
cin >> ini >> fim;
cout << solve(1, 0) << '\n';
return 0;
}
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
18 ms |
31980 KB |
Output isn't correct |
2 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
18 ms |
31980 KB |
Output isn't correct |
2 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
18 ms |
31980 KB |
Output isn't correct |
2 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Incorrect |
18 ms |
31980 KB |
Output isn't correct |
2 |
Halted |
0 ms |
0 KB |
- |