This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
const LL MOD = 1000000007;
int main(){
int n, k;
cin >> n >> k;
n--;
k--;
LL dp[n+1][n+1];
for(LL i = 0; i <= n; i++){
for(LL j = 0; j <= i; j++){
dp[i][j] = 0;
if(i == 0 && j == 0){
dp[i][j] = 1;
}
if(i > 0){
if(j > 0){
dp[i][j] += dp[i-1][j-1] * (i+1-j);
}
if(j < i){
dp[i][j] += dp[i-1][j] * (j+1);
}
}
dp[i][j] %= MOD;
}
}
cout << dp[n][k] << '\n';
}
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