Submission #1003280

#	Time	Username	Problem	Language	Result	Execution time	Memory
1003280		Sharky	Kangaroo (CEOI16_kangaroo)	C++17	0 / 100	0 ms	444 KiB

kangaroo

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

#define int long long
const int mod = 1000000007;

const int N = 2008;
int dp[N][N];

int32_t main() {
    int n, s, e, ep = 0;
    cin >> n >> s >> e;
    dp[1][1] = 1;
    if (s == 1 || e == 1) ep++;
    for (int i = 2; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
            if (i == s || i == e) {
                ep++;
                dp[i][j] = (dp[i - 1][j - 1] + dp[i - 1][j]) % mod;
            } else {
                dp[i][j] = (dp[i - 1][j - 1] * max(0LL, (j - ep)) % mod + dp[i - 1][j + 1] * j % mod) % mod;
            }
            // cout << i << ' ' << j << ' ' << dp[i][j] << '\n';
        }
    }
    cout << dp[n][1] << '\n';
}

// 1 5 2 4 3 6
// 1 3 2 5 4 6
// 1 4 2 5 3 6
// 1 5 3 4 2 6
// 1 4 3 5 2 6 

// 6
// 4 1 3 2 6 5
// 4 2 3 1 6 5
// 4 6 1 3 2 5
// 4 6 2 3 1 5

• Subtask 1: 0 / 6
• Subtask 2: 0 / 30
• Subtask 3: 0 / 15
• Subtask 4: 0 / 49