Submission #1118244

#	Time	Username	Problem	Language	Result	Execution time	Memory
1118244		vjudge1	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	36 ms	31836 KiB

kangaroo

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

typedef long long ll;

const int mod = 1e9 + 7;

int32_t main () {

    ios_base::sync_with_stdio(0); 
    cin.tie(0); 
    cout.tie(0); 

    int N, cs, cf, say = 0;
    cin >> N >> cs >> cf;
    vector<vector<ll>> dp(N + 1, vector<ll>(N + 1, 0));
    dp[0][0] = 1;
    for (int i = 0;i < N;i ++) {
        for (int j = 0;j <= i;j ++) {
            if (i + 1 == cs || i + 1 == cf) {
                say += (j == 0);
                dp[i + 1][j + 1] = (dp[i][j] + dp[i + 1][j + 1]) % mod;
                dp[i + 1][j] = (dp[i][j] + dp[i + 1][j]) % mod;
            } else {
                dp[i + 1][j + 1] = (dp[i][j] * max(0, (j + 1 - say)) + dp[i + 1][j + 1]) % mod;
                if (j - 1 >= 0) dp[i + 1][j - 1] = (dp[i][j] * (j - 1) + dp[i + 1][j - 1]) % mod;
            }
        }
    }
    // for (int i = 1;i <= N;i ++) {
    //     for (int j = 1;j <= i;j ++) {
    //         // for (int k = 0;k < 3;k ++) {
    //             cout << dp[i][j] << " ";
    //         // } cout << "\n";
    //     } cout << "\n";
    // } cout << "\n";
    cout << dp[N][1] << "\n";
}

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