Submission #1146931

#	Time	Username	Problem	Language	Result	Execution time	Memory
1146931		iah	Kangaroo (CEOI16_kangaroo)	C++20	100 / 100	5 ms	328 KiB

kangaroo

#include<bits/stdc++.h>
using namespace std;

#define NAME ""
#define ll long long
#define pii pair < int , int >
#define fi first
#define se second
#define FOR(i, a, b) for (int i = (a), _b = (b); i <= _b; i ++)
#define FORD(i, a, b) for (int i = (a), _b = (b); i >= _b; i --)
#define REP(i, n) for (int i = 0, _n = (n); i < _n; i ++)
#define bit(x, i) (((x) >> (i)) & 1ll)
#define mask(x) (1ll << (x))
#define mem(f, x) memset(f, x, sizeof(f))
#define sz(x) (int32_t) (x.size())

const int nmax = 2000;
const int mod = 1e9 + 7;
ll dp[2][nmax + 7];

signed main() {
  for(string s: {NAME, ""}) {
    if (fopen((s + ".inp").c_str(), "r")) {
      freopen((s + ".inp").c_str(), "r", stdin);
      freopen((s + ".out").c_str(), "w", stdout);
      break;
    }
  }
  cin.tie(0)->sync_with_stdio(0);

  int n, cs, cf;
  cin >> n >> cs >> cf;

  dp[1][1] = 1;

  FOR(i, 2, n) {
    FOR(j, 1, i) {
      dp[i % 2][j] = 0;
    }

    FOR(j, 1, i - 1) {
      if (i == cs || i == cf) {
        dp[i % 2][j] += dp[1 - i % 2][j];
        dp[i % 2][j] %= mod;
        dp[i % 2][j + 1] += dp[1 - i % 2][j];
        dp[i % 2][j + 1] %= mod;
      }
      else if (j + 1 > 0) {
        dp[i % 2][j + 1] += dp[1 - i % 2][j] * (j + 1 - (i > cs) - (i > cf));
        dp[i % 2][j + 1] %= mod;
        dp[i % 2][j - 1] += dp[1 - i % 2][j] * (j - 1);
        dp[i % 2][j - 1] %= mod;
      }
    }

//    cout << i << ":\n";
//    FOR(j, 1, i) {
//      cout << j << " " << dp[i % 2][j] << "\n";
//    }
  }

  cout << dp[n % 2][1];

  return 0;
}

Compilation message (stderr)

kangaroo.cpp: In function 'int main()':
kangaroo.cpp:24:14: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   24 |       freopen((s + ".inp").c_str(), "r", stdin);
      |       ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
kangaroo.cpp:25:14: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   25 |       freopen((s + ".out").c_str(), "w", stdout);
      |       ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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