Submission #993151

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Source Code Expand

#ifdef DEBUG
#define _GLIBCXX_DEBUG
#endif

#include <bits/stdc++.h>

using namespace std;

mt19937 mrand(random_device{} ()); 

int rnd(int x) {
  return mrand() % x;
}

typedef long double ld;
typedef long long ll;

#ifdef DEBUG
#define eprintf(...) fprintf(stderr, __VA_ARGS__), fflush(stderr)
#else
#define eprintf(...) ;
#endif

#define pb push_back
#define mp make_pair
#define sz(x) ((int) (x).size())
#define TASK "text"

const int inf = (int) 1.01e9;
const ld eps = 1e-9;
const ld pi = acos((ld) -1.0);

void precalc() {
}

const int mod = (int) 1e9 + 7;

void add(int &x, int y) {
  if ((x += y) >= mod) {
    x -= mod;
  }
}

int mult(int x, int y) {
  return (long long) x * y % mod;
}

int myPower(int x, int pw) {
  int res = 1;
  for (; pw; pw >>= 1) {
    if (pw & 1) {
      res = mult(res, x);
    }
    x = mult(x, x);
  }
  return res;
}

int n, m;

int read() {
  if (scanf("%d%d", &n, &m) < 2) {
    return 0;
  }
  return 1;
}

const int maxn = (int) 3e2 + 10;
int dp[2][maxn][maxn];

void solve() {
  memset(dp, 0, sizeof(dp));
  int rot = 0;
  dp[rot][1][1] = 1;
  for (int iter = 1; iter <= m; ++iter) {
    memset(dp[!rot], 0, sizeof(dp[!rot]));
    for (int j = 1; j <= n; ++j) {
      for (int into = 1; into <= j; ++into) {
        int cur = dp[rot][j][into];
        if (!cur) {
          continue;
        }
        if (j < n) {
          add(dp[!rot][j + 1][into], mult(cur, n - j));
        }
        add(dp[!rot][j][into], mult(cur, j - into));
        add(dp[!rot][j][j], mult(cur, into));
      }
    }
    rot = !rot;
  }
  printf("%d\n", dp[rot][n][n]);
}

int main() {
  precalc();
#ifdef LOCAL
  freopen(TASK ".out", "w", stdout);
  assert(freopen(TASK ".in", "r", stdin));
#endif

  while (1) {
    if (!read()) {
      break;
    }
    solve();
#ifdef DEBUG
    eprintf("Time %.2f\n", (double) clock() / CLOCKS_PER_SEC);
#endif
  }
  return 0;
}

Submission Info

Judge Result