24 lines
423 B
C++
24 lines
423 B
C++
#include <iostream>
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#include <cstdio>
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#define N 1005
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#define mod 1000000007
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#define ll __int64
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using namespace std;
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ll f[N][N];
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void init()
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{
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int i,j;
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for (i=1;i<N;i++)
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{
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f[i][0]=1;
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for (j=1;j<i;j++) f[i][j]=((j+1)*f[i-1][j]+(i-j)*f[i-1][j-1])%mod;
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}
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}
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int main()
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{
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int n,k;
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init();
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while (scanf("%d%d",&n,&k)!=EOF) cout<<f[n][k]<<endl;
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return 0;
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}
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