Submission #5555040

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Source Code Expand

#include<bits/stdc++.h>
using namespace std;
#define int long long
#define fi first
#define se second
#define pb push_back
#define sz(x) ((int)(x).size())
#define all(x) x.begin(),x.end()
#define dmp(x) cerr<<#x<<":"<<x<<endl
#define FOR(i,a,b) for(int i=(int)a,c=(int)b;i<c;++i)
#define rep(i,b) FOR(i,0,b)
#define ROF(i,a,b) for(int i=b-1,c=(int)a;i>=c;--i)
#define per(i,b) ROF(i,0,b)
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}
int dp[2][333][333];
signed main(){
  int n,m,mod=1000000007;
  cin>>n>>m;
  dp[0][1][n-1]=1;
  for(int i=0;i<m;i++){
    int ii=i%2;
    int ni=(i+1)%2;
    fill_n(*dp[ni],333*333,0);
    for(int j=0;j<=n;j++){
	 for(int k=0;k<n;k++){
	   if(dp[ii][j][k]==0)continue;
	   dp[ni][n-k][k]+=dp[ii][j][k]*j%mod;
	   dp[ni][n-k][k]%=mod;
	   dp[ni][j][k]+=dp[ii][j][k]*(n-k-j)%mod;
	   dp[ni][j][k]%=mod;
	   if(k>0){
		dp[ni][j][k-1]+=dp[ii][j][k]*k%mod;
		dp[ni][j][k-1]%=mod;
	   }
	 }
    }
  }
  cout<<dp[m%2][n][0]<<endl;
  return 0;
}

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