Submission #1220911

#	Time	Username	Problem	Language	Result	Execution time	Memory
1220911		QuocSensei	Kangaroo (CEOI16_kangaroo)	C++20	100 / 100	45 ms	31816 KiB

kangaroo

#include <bits/stdc++.h>

#define ll long long
#define el cout << '\n'

using namespace std;

const int maxn = 2e3;
const int MOD = 1e9 + 7;

int n, s, t;
ll dp[maxn + 10][maxn + 10];

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

int main()
{
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    if (fopen("KANGAROO.INP", "r"))
    {
        freopen("KANGAROO.INP", "r", stdin);
        freopen("KANGAROO.OUT", "w", stdout);
    }

    cin >> n >> s >> t;
    dp[0][0] = 1;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
        {
            if (i == s)
            {
                add(dp[i][j], dp[i - 1][j - 1]);
                if (i > t && i < n)
                    add(dp[i][j], (j - 1) * dp[i - 1][j]);
                else if (i > t)
                    add(dp[i][j], dp[i - 1][j]);
                else
                    add(dp[i][j], j * dp[i - 1][j]);
            }
            else if (i == t)
            {
                add(dp[i][j], dp[i - 1][j - 1]);
                if (i > s && i < n)
                    add(dp[i][j], (j - 1) * dp[i - 1][j]);
                else if (i > s)
                    add(dp[i][j], dp[i - 1][j]);
                else
                    add(dp[i][j], j * dp[i - 1][j]);
            }
            else
            {
                add(dp[i][j], dp[i - 1][j - 1]);
                if (i > max(s, t) && i < n)
                    add(dp[i][j], j * (j - 1) * dp[i - 1][j + 1]);
                else if (i > max(s, t))
                    add(dp[i][j], dp[i - 1][j + 1]);
                else if (i > min(s, t))
                    add(dp[i][j], j * j * dp[i - 1][j + 1]);
                else
                    add(dp[i][j], j * (j + 1) * dp[i - 1][j + 1]);
            }
        }
//    for (int i = 1; i <= n; i++)
//    {
//        for (int j = 1; j <= n; j++)
//            cout << dp[i][j] << ' ';
//        el;
//    }
    cout << dp[n][1];
}

Compilation message (stderr)

kangaroo.cpp: In function 'int main()':
kangaroo.cpp:27:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   27 |         freopen("KANGAROO.INP", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
kangaroo.cpp:28:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   28 |         freopen("KANGAROO.OUT", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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