#include <bits/stdc++.h>
using namespace std;
using lint = long long;
const int MAX_N = 2e3 + 5;
const lint MOD = 1e9 + 7;
int n;
int s, f;
lint mod(lint x) {
return x % MOD;
}
lint dp[MAX_N][MAX_N];
void do_dp() {
dp[1][1] = 1;
for (int i = 1; i < n; i++) {
for (int c = 1; c <= n; c++) {
// cout << i << ", " << c << ": " << dp[i][c] << endl;
if ((i + 1) == s || (i + 1) == f) {
dp[i + 1][c + 1] = mod(dp[i + 1][c + 1] + dp[i][c]);
dp[i + 1][c] = mod(dp[i + 1][c] + dp[i][c]);
continue;
}
lint mult = c + 1;
mult -= (bool) (i > s);
mult -= (bool) (i > f);
dp[i + 1][c + 1] = mod(dp[i + 1][c + 1] + mod(dp[i][c] * mult));
dp[i + 1][c - 1] = mod(dp[i + 1][c - 1] + mod(dp[i][c] * (c - 1)));
}
}
}
int main() {
// freopen("kangaroo.in", "r", stdin);
cin >> n >> s >> f;
if (s > f) swap(s, f);
do_dp();
cout << dp[n][1] << '\n';
}
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
0 ms |
348 KB |
Output is correct |
2 |
Incorrect |
0 ms |
348 KB |
Output isn't correct |
3 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
0 ms |
348 KB |
Output is correct |
2 |
Incorrect |
0 ms |
348 KB |
Output isn't correct |
3 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
0 ms |
348 KB |
Output is correct |
2 |
Incorrect |
0 ms |
348 KB |
Output isn't correct |
3 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
0 ms |
348 KB |
Output is correct |
2 |
Incorrect |
0 ms |
348 KB |
Output isn't correct |
3 |
Halted |
0 ms |
0 KB |
- |