Submission #1118228

#	Time	Username	Problem	Language	Result	Execution time	Memory
1118228		vjudge1	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	14 ms	31568 KiB

kangaroo

#include <bits/stdc++.h>
using namespace std;
# define int long long
const int mod = 1e9 + 7;

int dp[2001][2001];

void solve()
{
  int n, cf, cn, cnt = 0;
  cin >> n >> cf >> cn;
  dp[1][1] = 1;
  for(int i = 1; i <= n; i++)
  {
    if(i == cf || i == cn)
      cnt++;
    for(int j = 1; j < i; j++)
    {
      if(i == cf || i == cn)
      {
        dp[i][j] += (dp[i - 1][j]) % mod;
        dp[i][j + 1] += (dp[i - 1][j] % mod);
      }
      else
      {
        dp[i][j + 1] += (dp[i - 1][j] * (j + 1 - cnt)) % mod;
        dp[i][j - 1] += (dp[i - 1][j] * (j - 1)) % mod;
      }
    }
  }
  cout << dp[n][1] << endl;
}

signed main()
{
  int tt = 1;
  // cin >> tt;
  while(tt--)
    solve();
}

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