#include<iostream>
#include<vector>
#include<map>
#include<set>
#include<cassert>
#include<cassert>
#include<unordered_map>
#include<unordered_set>
#include<functional>
#include<queue>
#include<stack>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<sstream>
#include<iomanip>
#include<cstdio>
#include<cstdlib>
#include<numeric>
#include<random>
#include<chrono>
#include<bitset>
using namespace std;
#define all(x) (x).begin(), (x).end()
#define pb push_back
#define xx first
#define yy second
#define sz(x) (int)(x).size()
#define gc getchar
#define IO ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#define mp make_pair
#ifndef ONLINE_JUDGE
# define LOG(x) (cerr << #x << " = " << (x) << endl)
#else
# define LOG(x) ((void)0)
#endif
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
const double PI=acos(-1);
const ll INF = 1LL<<62;
const ll MINF = -(1LL<<62);
template<typename T> T getint() {
T val=0;
char c;
bool neg=false;
while((c=gc()) && !(c>='0' && c<='9')) {
neg|=c=='-';
}
do {
val=(val*10)+c-'0';
} while((c=gc()) && (c>='0' && c<='9'));
return val*(neg?-1:1);
}
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count()); uniform_int_distribution<int>(0, n-1)(rng)
const ll mod=1e9+7;
ll dp[2001][2001];
int main() {
IO;
ll n,st,en;
cin>>n>>st>>en;
dp[1][1]=1;
for(ll i=2;i<=n;++i) {
for(ll j=1;j<=i;++j) {
int cnt=(i>=st)+(i>=en);
if(i==st) {
//~ LOG(j);
//~ LOG(j-cnt+1);
dp[i][j]=(dp[i][j]+dp[i-1][j]*(j-cnt+1))%mod;
dp[i][j]=(dp[i][j]+dp[i-1][j-1])%mod;
}else if(i==en) {
dp[i][j]=(dp[i][j]+dp[i-1][j]*(j-cnt+1))%mod;
dp[i][j]=(dp[i][j]+dp[i-1][j-1])%mod;
}else {
dp[i][j]=(dp[i][j]+dp[i-1][j+1]*((j+1)*j-(i>=st)*j-(i>=en)*j+1*(i>=st&&i>=en)))%mod;
dp[i][j]=(dp[i][j]+dp[i-1][j-1])%mod;
}
}
}
//~ LOG(dp[1][1]);
//~ LOG(dp[2][2]);
//~ LOG(dp[3][1]);
//~ LOG(dp[3][2]);
//~ LOG(dp[3][3]);
//~ LOG(dp[4][1]);
//~ LOG(dp[4][2]);
//~ LOG(dp[4][3]);
//~ LOG(dp[4][4]);
cout<<dp[n][1]<<"\n";
return 0;
}
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
0 ms |
384 KB |
Output is correct |
2 |
Correct |
0 ms |
384 KB |
Output is correct |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
0 ms |
384 KB |
Output is correct |
2 |
Correct |
0 ms |
384 KB |
Output is correct |
3 |
Incorrect |
0 ms |
512 KB |
Output isn't correct |
4 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
0 ms |
384 KB |
Output is correct |
2 |
Correct |
0 ms |
384 KB |
Output is correct |
3 |
Incorrect |
0 ms |
512 KB |
Output isn't correct |
4 |
Halted |
0 ms |
0 KB |
- |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
0 ms |
384 KB |
Output is correct |
2 |
Correct |
0 ms |
384 KB |
Output is correct |
3 |
Incorrect |
0 ms |
512 KB |
Output isn't correct |
4 |
Halted |
0 ms |
0 KB |
- |