Submission #425476

#	Time	Username	Problem	Language	Result	Execution time	Memory
425476		Lam_lai_cuoc_doi	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	54 ms	29764 KiB

kangaroo

#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using ld = long double;
using ull = unsigned long long;

constexpr bool typetest = 0;
constexpr int N = 2e3 + 2;
constexpr int mod = 1e9 + 7;
int n, cs, cf, v;
int dp[N][N], f1[N][N];

void Read()
{
    cin >> n >> cs >> cf;
    if (cs > cf)
        swap(cs, cf);
    v = n - cf;
}

ll f(int n, int i)
{
    if (dp[n][i] != -1)
        return dp[n][i];
    if (i == 1)
        return dp[n][i] = (f1[n][n - v] + mod) % mod;
    if (i == 2)
        return dp[n][i] = ((f1[n][n - v] + f1[n - 1][n - 1 - v]) % mod + mod) % mod;

    return dp[n][i] = (((2 * f(n, i - 1) % mod - f(n, i - 2)) % mod - f(n - 2, i - 2)) % mod + mod) % mod;
}

void Solve()
{
    f1[2][2] = 1;
    for (int i = 3; i <= n; ++i)
    {
        if (i & 1)
            for (int j = 2; j < n; ++j)
                (f1[i][2] += f1[i - 1][j]) %= mod;

        for (int j = 3; j <= i; ++j)
            f1[i][j] = (((i & 1) ? f1[i][j - 1] - f1[i - 1][j - 1] : f1[i][j - 1] + f1[i - 1][j - 1]) % mod + mod) % mod;

        /*cout << i << ": ";
        for (int j = 1; j <= i; ++j)
            cout << f1[i][j] << " ";

        cout << "\n";*/
    }
    memset(dp, -1, sizeof dp);
    cout << (f(n, cs) % mod + mod) % mod;
}

int32_t main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int t(1);
    if (typetest)
        cin >> t;
    for (int _ = 1; _ <= t; ++_)
    {
        Read();
        Solve();
    }
}

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