Submission #869130

#	Time	Username	Problem	Language	Result	Execution time	Memory
869130		mgl_diamond	Kangaroo (CEOI16_kangaroo)	C++17	6 / 100	0 ms	604 KiB

kangaroo

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ii = pair<int, int>;
 
#define foru(i, l, r) for(int i=(l); i<=(r); ++i)
#define ford(i, l, r) for(int i=(l); i>=(r); --i)
#define fore(x, v) for(auto &x : v)
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
#define fi first
#define se second
#define file "input"

void setIO() {
  ios::sync_with_stdio(0);
  cin.tie(0); cout.tie(0);
  if (fopen(file".inp", "r")) {
    freopen(file".inp", "r", stdin);
    freopen(file".out", "w", stdout);
  }
}

const int N = 2002, MOD = 1e9+7;
int n, s, t, f[N][N][2][2];
int ans;

void add(int &a, int b) {
  a += b;
  if (a >= MOD) a -= MOD;
}

int mul(int a, int b) {
  return 1LL * a * b % MOD;
}

int nc2(int n) {
  return (n * (n-1) / 2) % MOD;
}

int main() {
  setIO();

  cin >> n >> s >> t;

  if (n == 2) {
    cout << 1;
    return 0;
  }

  f[0][0][0][0] = 1;

  foru(i, 0, n-1) 
  foru(cc0, 0, i) 
  foru(cc1, 0, 1) 
  foru(cc2, 0, 1) {
    int ret = f[i][cc0][cc1][cc2];
    if (ret == 0) continue;
    // cout << i << " " << cc0 << " " << cc1 << " " << cc2 << " " << ret << "\n";

    if (i+1 == s) {
      add(f[i+1][cc0][1][cc2], ret);
      if (cc0 > 0) add(f[i+1][cc0-1][1][cc2], mul(ret, cc0));
      continue;
    }

    if (i+1 == t) {
      add(f[i+1][cc0][cc1][1], ret);
      if (cc0 > 0) add(f[i+1][cc0-1][cc1][1], mul(ret, cc0));
      continue; 
    }

    add(f[i+1][cc0+1][cc1][cc2], ret);
    if (cc0 > 1) add(f[i+1][cc0-1][cc1][cc2], mul(mul(cc0, cc0-1), ret));
    if (cc1 && cc0 > 0) add(f[i+1][cc0-1][cc1][cc2], mul(ret, cc0));
    if (cc2 && cc0 > 0) add(f[i+1][cc0-1][cc1][cc2], mul(ret, cc0));
  }

  // cout << f[n][0][1][1] << "\n";
  // cout << f[n-1][0][1][0];
  if (t == n) cout << f[n-1][0][1][0];
  else cout << f[n-1][0][1][1];
}

Compilation message (stderr)

kangaroo.cpp: In function 'void setIO()':
kangaroo.cpp:19:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   19 |     freopen(file".inp", "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
kangaroo.cpp:20:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   20 |     freopen(file".out", "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 6 / 6
• Subtask 2: 0 / 30
• Subtask 3: 0 / 15
• Subtask 4: 0 / 49