Submission #994237

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Source Code Expand

#include <bits/stdc++.h>
typedef long long LL;
#define SORT(c) sort((c).begin(),(c).end())
 
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
 
using namespace std;
const LL prime=1000000007;
int n;
LL memo[310][310][310];
LL solve(int left,int already,int goals){
  if(left==0)
    if(goals==n) return 1;
    else return 0;
  else if(memo[left][already][goals]!=-1) return memo[left][already][goals];
  else{
    LL answer=0;
    if(n-already-goals) answer+=solve(left-1,already+1,goals)*(n-already-goals);
    answer+=solve(left-1,already,goals)*already;
    answer+=solve(left-1,0,already+goals)*goals;
    return memo[left][already][goals]=answer%prime;
  }
}
int main(void)
{
  int m;
  cin >> n >> m;
  REP(i,301) REP(j,301) REP(k,301) memo[i][j][k]=-1;
  cout << solve(m,0,1) << endl;
  return 0;
}

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