Submission #1914191

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Source Code Expand

#include <bits/stdc++.h>

using namespace std;

const int mod = 1e9 + 7;

int N, M;
int dp[301][301][301];

int rec(int step, int sc1, int out)
{
  if(step == M) return (sc1 == N);
  if(~dp[step][sc1][out]) return (dp[step][sc1][out]);
  int ret = 0;
  if(sc1 + out + 1 <= N) {
    (ret += 1LL * rec(step + 1, sc1, out + 1) * (N - sc1 - out) % mod) %= mod;
  }
  if(out > 0) {
    (ret += 1LL * rec(step + 1, sc1, out) * out % mod) %= mod;
  }
  (ret += 1LL * rec(step + 1, sc1 + out, 0) * sc1 % mod) %= mod;
  return (dp[step][sc1][out] = ret);
}

int main()
{
  cin >> N >> M;
  memset(dp, -1, sizeof(dp));
  cout << rec(0, 1, 0) << endl;
}

Submission Info

Judge Result