Submission #598776

#	Time	Username	Problem	Language	Result	Execution time	Memory
598776		minhnguyent546	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	23 ms	16060 KiB

kangaroo

#include <bits/stdc++.h>
#define uint unsigned int
#define ll long long
#define ull unsigned long long
#define sqr(a) (1LL * (a) * (a))
using namespace std;

#ifdef LOCAL
#include <bug.h>
#else
#define mt(...)
#endif

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

const int mod = 1000000007;
const int inf = 0x3f3f3f3f;

// https://oj.uz/problem/view/CEOI16_kangaroo
// https://github.com/stefdasca/CompetitiveProgramming/blob/master/CEOI/CEOI%2016-Kangaroo.cpp
// https://codeforces.com/blog/entry/47764?#comment-704139
//-----------------------------------------------------------------------//

int main() {
    ios::sync_with_stdio(false); cin.tie(nullptr);
    // freopen("input.txt", "r", stdin);
    // freopen("output.txt", "w", stdout);

    int n, s, e;
    cin >> n >> s >> e;
    vector<vector<int>> dp(n + 1, vector<int>(n + 1));
    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 {
                int a = 1LL * dp[i - 1][j + 1] * j % mod; // merge two components
                int subtract = 0;
                if (i > s) ++subtract;
                if (i > e) ++subtract;
                int b = 1LL * dp[i - 1][j - 1] * (j - subtract) % mod; // create new component
                dp[i][j] = a + b;
            }   
            dp[i][j] %= mod;
        }
    }
    cout << dp[n][1] << '\n';
        

    return 0;
}

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