Submission #565689

#	Time	Username	Problem	Language	Result	Execution time	Memory
565689		piOOE	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	15 ms	14080 KiB

kangaroo

#include <bits/stdc++.h>

using namespace std;

#define all(x) begin(x), end(x)
#define sz(x) ((int)size(x))
#define trace(x) cout << #x << ": " << (x) << endl;

typedef long long ll;

const int mod = 1'000'000'007, maxN = 2001;

int add(int a, int b) {
    return a + b < mod ? a + b : a + b - mod;
}

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

int dp[maxN][maxN];
//dp[i][number of blocks]

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int N, S, T;
    cin >> N >> S >> T;
    dp[1][1] = 1;
    for (int i = 2; i <= N; ++i) {
        for (int j = 1; j <= i; ++j) {
            if (i == S || i == T) {
                dp[i][j] = add(dp[i - 1][j - 1], dp[i - 1][j]);
            } else {
                dp[i][j] = add(mul(dp[i - 1][j - 1], j - (S < i) - (T < i)), mul(dp[i - 1][j + 1], j));
            }
        }
    }
    cout << dp[N][1];
    return 0;
}

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