Submission #228896

#	Time	Username	Problem	Language	Result	Execution time	Memory
228896		quocnguyen1012	Kangaroo (CEOI16_kangaroo)	C++14	100 / 100	58 ms	14200 KiB

kangaroo

#include <bits/stdc++.h>

#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define ar array

using namespace std;
typedef long long ll;
typedef pair<int, int> ii;

const int maxn = 2e3 + 5, mod = 1e9 + 7;

int N, cs, cf, f[maxn][maxn];

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

signed main(void)
{
  ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  #ifdef LOCAL
    freopen("A.INP", "r", stdin);
    freopen("A.OUT", "w", stdout);
  #endif // LOCAL
  cin >> N >> cs >> cf;
  if(cs > cf) swap(cs, cf);
  f[1][0] = 1;
  for(int i = 1; i <= N; ++i){
    for(int j = 0; j <= i; ++j){
      if(i == cs || i == cf){
        add(f[i + 1][j], f[i][j]);
        if(j > 0) add(f[i + 1][j - 1], 1ll * f[i][j] * j % mod);
      }
      else{
        if(i > cs && j > 0){
          add(f[i + 1][j - 1], 1ll * f[i][j] * j % mod);
        }
        if(i > cf && j > 0){
          add(f[i + 1][j - 1], 1ll * f[i][j] * j % mod);
        }
        add(f[i + 1][j + 1], f[i][j]);
        if(j > 1) add(f[i + 1][j - 1], 1ll * j * (j - 1) % mod * f[i][j] % mod);
      }
    }
  }
  cout << f[N][0];
}

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