Submission #591329

#	Time	Username	Problem	Language	Result	Execution time	Memory
591329		messiuuuuu	Kangaroo (CEOI16_kangaroo)	C++14	0 / 100	1 ms	340 KiB

kangaroo

#include<bits/stdc++.h>
#define task "C"
#define ll long long
#define ld long double
#define fi first
#define se second
#define pb push_back
using namespace std;
const int MAXN = 2e3 + 5;
const ll INF = 1e18 + 5;
const int MOD = 1e9 + 7;

int n, cs, cf;

void Input()
{
    cin >> n >> cs >> cf;
}

int dp[MAXN][MAXN];

void add(int& a, int b)
{
    a += b;
    if (a > MOD)
        a -= MOD;
}

int mul(int a, int b)
{
    return 1ll * a * b % MOD;
}

void Solve()
{
    if (cs > cf)
        swap(cs, cf);
    dp[0][0] = 1;
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j <= i; j++)
        {
            if (i + 1 == cs || i + 1 == cf)
            {
                add(dp[i + 1][j], dp[i][j]);
                if (j > 0)
                    add(dp[i + 1][j - 1], mul(dp[i][j], j));
            } else
            {
                add(dp[i + 1][j + 1], dp[i][j]);

                if (j > 0)
                    add(dp[i + 1][j - 1], mul(dp[i][j], mul(j, j - 1)));

                if (i > cs && j > 0)
                    add(dp[i + 1][j - 1], mul(dp[i][j], j));

                if (i > cf && j > 0)
                    add(dp[i + 1][j - 1], mul(dp[i][j], j));
            }
        }
    }
    cout << dp[n][1];
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    if (fopen(task".INP","r"))
    {
        freopen(task".INP","r",stdin);
        //freopen(task".OUT","w",stdout);
    }
    Input();
    Solve();
}

Compilation message (stderr)

kangaroo.cpp: In function 'int main()':
kangaroo.cpp:72:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   72 |         freopen(task".INP","r",stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 6
• Subtask 2: 0 / 30
• Subtask 3: 0 / 15
• Subtask 4: 0 / 49