Submission #909830

#	Time	Username	Problem	Language	Result	Execution time	Memory
909830		fanwen	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	18 ms	16056 KiB

kangaroo

#include <iostream>

using namespace std;

const int N = 2000 + 5;
const int Mod  = 1e9 + 7;

int n, s, e, dp[N][N];

int main() {
    cin >> n >> s >> e;
    dp[0][0] = 1;
    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j <= i; ++j) {
            if(i == s || i == e) {
                dp[i][j] = dp[i - 1][j - 1] + dp[i - 1][j];
            } else {
                dp[i][j] = (1LL * dp[i - 1][j + 1] * j % Mod + 1LL * dp[i - 1][j - 1] * (j - (i > s) - (i > e)) % Mod);
            }
            if(dp[i][j] >= Mod) dp[i][j] -= Mod;
        }
    }
    cout << dp[n][1];
}

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