제출 #493911

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
493911		khoabright	캥거루 (CEOI16_kangaroo)	C++17	100 / 100	23 ms	22980 KiB

kangaroo

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

#define int long long
#define ll long long
#define pii pair<int, int>
#define ff first
#define ss second
#define pb push_back
#define rep(i, a, b) for (int i = (int)a; i <= (int)b; ++i)
#define rep1(i, a, b) for (int i = (int)a; i >= (int)b; --i)
#define all(x) x.begin(), x.end()

const int N = 2e3 + 5;
const int mod = 1e9 + 7;

int dp[N][N];

signed main() {
    int n, a, b; cin >> n >> a >> b;
    dp[1][1] = 1;
    rep(i, 1, n - 1) rep(j, 1, i) {
        if (i + 1 == a || i + 1 == b) {
            (dp[i + 1][j] += dp[i][j]) %= mod;
            (dp[i + 1][j + 1] += dp[i][j]) %= mod;
        }

        else {
            // merge two components
            (dp[i + 1][j - 1] += dp[i][j] * (j - 1)) %= mod;

            // create a new component
            (dp[i + 1][j + 1] += (dp[i][j] * (j + 1 - (i + 1 > a) - (i + 1 > b)))) %= mod;
        }
    }

    cout << dp[n][1];
}

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