Submission #1216536

#	Time	Username	Problem	Language	Result	Execution time	Memory
1216536		arwakhattab	Kangaroo (CEOI16_kangaroo)	C++20	100 / 100	51 ms	15944 KiB

kangaroo

#include <bits/stdc++.h>
#define all(x) begin(x), end(x)
using namespace std;
using ll = long long;
const char nl = '\n', sp = ' ';

const int mod = 1e9 + 7;

inline int add(int a, int b) {
    return (__int128(a) + b) % mod;
}

inline int mul(int a, int b) {
    return (__int128(a) * b) % mod;
}

void solve() {
    int n, f, l;
    cin >> n >> f >> l;
    vector dp(n + 1, vector<int>(n + 1));
    dp[0][0] = 1;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
            if (i == f || i == l) {
                dp[i][j] = add(dp[i - 1][j], dp[i - 1][j - 1]);
            } else {
                int pos = j - (i > f) - (i > l);
                if (pos > 0) dp[i][j] = mul(dp[i - 1][j - 1], pos);
                if (j + 1 <= n) dp[i][j] = add(dp[i][j], mul(dp[i - 1][j + 1], j));
            }
        }
    }
    cout << dp[n][1] << nl;
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

#ifdef LOCAL
    freopen("../in.txt", "r", stdin);
    freopen("../out.txt", "w", stdout);
#endif

    int t = 1;
    // cin >> t;
    while (t--) {
        solve();
    }
}

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