Submission #469744

#	Time	Username	Problem	Language	Result	Execution time	Memory
469744		TheScrasse	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	41 ms	31772 KiB

kangaroo

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

#define nl "\n"
#define nf endl
#define ll long long
#define pb push_back
#define _ << ' ' <<

#define INF (ll)1e18
#define mod 1000000007
#define maxn 2010

ll i, i1, j, k, k1, t, n, m, res, flag[10], a, b;
ll st, nd, dp[maxn][maxn];

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

    #if !ONLINE_JUDGE && !EVAL
        ifstream cin("input.txt");
        ofstream cout("output.txt");
    #endif

    cin >> n >> st >> nd;

    if (n == 2) {
        cout << 1 << nl; return 0;
    }

    dp[1][1] = 1;
    for (i = 1; i <= n; i++) {
        if (i == st || i == nd) k++;
        if (i == 1) continue;
        for (j = 0; j <= n; j++) {
            if (i == st || i == nd) {
                if (j >= 1) dp[i][j] += dp[i - 1][j - 1];
                if (st + nd != 3) dp[i][j] += dp[i - 1][j];
            } else {
                if (j >= 1) dp[i][j] += (max((ll)0, j - k) * dp[i - 1][j - 1]);
                dp[i][j] += (j * dp[i - 1][j + 1]);
            }
            dp[i][j] %= mod;
        }
    }

    /* for (i = 1; i <= n; i++) {
        for (j = 1; j <= n; j++) {
            cout << dp[i][j] << ' ';
        }
        cout << nl;
    } */

    cout << dp[n][1] << nl;

    return 0;
}

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