Submission #1632380

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Source Code Expand

#include <bits/stdc++.h>
#define mset(a,b) memset(a,b,sizeof a)
#define mcpy(a,b) memcpy(a,b,sizeof b)
#define lb(x) ((x)&(-(x)))
#define xx first
#define yy second
#define pb push_back
#define mp make_pair
#define pii pair<int,int> 
#define dalao 1000000007
#define inf 0x3f3f3f3f
#define N 305
using namespace std;
typedef long long ll;
int n,m,f[N][N][N];
inline void upd(int& a,int b){a=a+b>=dalao?a+b-dalao:a+b;}
int main(){
	cin>>n>>m,f[0][1][1]=1;
	for(int i=0;i<m;i++)for(int j=1;j<=n;j++)for(int k=1;k<=j;k++)if(f[i][j][k])
		upd(f[i+1][j+1][k],1ll*f[i][j][k]*(n-j)%dalao),
		upd(f[i+1][j][k],1ll*f[i][j][k]*(j-k)%dalao),
		upd(f[i+1][j][j],1ll*f[i][j][k]*k%dalao);
	printf("%d",f[m][n][n]);
	return 0;
}

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