/*
https://oj.uz/problem/view/CEOI16_kangaroo
*/
#include<bits/stdc++.h>
#define int long long
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int rnd(int l,int r){return l+rng()%(r-l+1);}
#define forinc(a,b,c) for(int a=b, _c=c; a<=_c; ++a)
#define fordec(a,b,c) for(int a=b, _c=c; a>=_c; --a)
#define forv(a,b) for(auto &a:b)
#define fasty ios_base::sync_with_stdio(false),cin.tie(0),cout.tie(0)
#define ar array
#define ii pair<int,int>
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
#define all(a) begin(a),end(a)
#define reset(f,x) memset(f,x,sizeof(f))
#define bit(x,i) (x>>(i-1)&1ll)
#define on(x,i) (x|(1ll<<(i-1)))
#define off(x,i) (x&~(1ll<<(i-1)))
const int N=2005;
const int mod=1e9+7;
int n,cs,cf;
int f[N][N];
void add(int &x,int y){
x=(x+y);
if(x>=mod) x-=mod;
}
int32_t main(){
fasty;
#ifdef LOCAL
freopen("in.txt", "r", stdin);
#endif // LOCAL
cin>>n>>cs>>cf;
if(cs>cf) swap(cs,cf);
f[1][0]=1;
forinc(i,1,n){
forinc(j,0,i){
if(i==cs || i==cf){
add(f[i+1][j], f[i][j]);
if(j) add(f[i+1][j-1], f[i][j]);
} else{
if(j>1) add(f[i+1][j-1], j*(j-1)%mod*f[i][j]%mod);
if(i>cs && j) add(f[i+1][j-1], f[i][j]*j%mod);
if(i>cf && j) add(f[i+1][j-1], f[i][j]*j%mod);
add(f[i+1][j+1], f[i][j]);
}
}
}
cout<<f[n][0];
}
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
384 KB |
Output is correct |
| 2 |
Incorrect |
0 ms |
384 KB |
Output isn't correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
384 KB |
Output is correct |
| 2 |
Incorrect |
0 ms |
384 KB |
Output isn't correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
384 KB |
Output is correct |
| 2 |
Incorrect |
0 ms |
384 KB |
Output isn't correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
384 KB |
Output is correct |
| 2 |
Incorrect |
0 ms |
384 KB |
Output isn't correct |
