Submission #307653

#	Time	Username	Problem	Language	Result	Execution time	Memory
307653		Elephant52	Kangaroo (CEOI16_kangaroo)	C++11	100 / 100	63 ms	31608 KiB

kangaroo

#include<bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<pair<int, int> > vpi;

#define INF 1000000000
#define F first
#define S second
#define PB push_back
#define MP make_pair
#define rep(i,a,b) for (ll i = a; i < b; i++)

void setIO(string name) {
    freopen((name+".in").c_str(), "r", stdin); 
    freopen((name+".out").c_str(), "w", stdout);
}

int N, A, B;

int mod = 1e9 + 7;

ll dp[2001][2001];

int main() {
    ios::sync_with_stdio(0); cin.tie(0);

    cin >> N >> A >> B;
    
    dp[1][1] = 1;
    
    rep(i,2,N+1) {
        rep(j,1,N+1) {
            if (i == A || i == B) dp[i][j] = (dp[i-1][j] + dp[i-1][j-1]) % mod;
            else dp[i][j] = j * dp[i-1][j+1] % mod + dp[i-1][j-1] * (j - (i > A) - (i > B)) % mod;
        }
    }
    
    cout << dp[N][1] << endl;
       
    return 0;
}

Compilation message (stderr)

kangaroo.cpp: In function 'void setIO(std::string)':
kangaroo.cpp:18:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
   18 |     freopen((name+".in").c_str(), "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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((name+".out").c_str(), "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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