제출 #680883

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
680883		vjudge1	캥거루 (CEOI16_kangaroo)	C++14	100 / 100	36 ms	16204 KiB

kangaroo

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

#define F first
#define S second
#define pb push_back
#define all(a) a.begin(), a.end()

typedef long long ll;
typedef pair<int, int> ii;

const int N = 2000 + 5;
const int mod = 1e9 + 7;
int n, s, t;
int f[N][N];

void fix(int &a)
{
    if(a >= mod) a -= mod;
    if(a < 0) a += mod;
}

int dp(int i, int j)
{
    if(j < 0) return 0;
    if(i > n) return j == 1;
    int &res = f[i][j];
    if(~res) return res;
    
    res = 0;
    if(i == s || i == t)
        res += dp(i + 1, j) + dp(i + 1, j + 1), fix(res);
    else
    {
        res += 1LL * dp(i + 1, j - 1) * (j - 1) % mod, fix(res);
        res += 1LL * dp(i + 1, j + 1) * (j + 1 - (i > s) - (i > t)) % mod, fix(res);
    }
    return res;
}

void solve()
{
    cin >> n >> s >> t;
    if(s > t) swap(s, t);
    memset(f, -1, sizeof f);
    cout << dp(1, 0);
}

signed main()
{
    cin.tie(0)->sync_with_stdio(0);
    int t = 1;
    // cin >> t;
    while(t--) solve();
    return 0;
}

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