Submission #115965

#	Time	Username	Problem	Language	Result	Execution time	Memory
115965		IOrtroiii	Kangaroo (CEOI16_kangaroo)	C++14	100 / 100	27 ms	14208 KiB

kangaroo

#include <bits/stdc++.h>

using namespace std;

const int N = 2020;
const int mod = 1000000007;

int f[N][N];

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

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

int main() {
   ios_base::sync_with_stdio(false); cin.tie(0);
   int n, cs, cf;
   cin >> n >> cs >> cf;
   f[1][1] = 1;
   for (int i = 2; i <= n; ++i) {
      for (int j = 1; j < i; ++j) {
         if (i == cs || i == cf) {
            add(f[i][j], f[i - 1][j]);
            add(f[i][j + 1], f[i - 1][j]);
         } else {
            if (j >= 2) add(f[i][j - 1], mul(f[i - 1][j], j - 1));
            int k = j - (i > cs) - (i > cf) + 1;
            add(f[i][j + 1], mul(f[i - 1][j], k));
         }
      }
   }
   cout << f[n][1] << '\n';
}

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