Submission #505035

#	Time	Username	Problem	Language	Result	Execution time	Memory
505035		lethinh05	Kangaroo (CEOI16_kangaroo)	C++11	100 / 100	20 ms	22944 KiB

kangaroo

#include <bits/stdc++.h>

#define oo 1000000007
#define ll long long
#define ld long double
#define ii pair<int, int>
#define pll pair<ll, ll>
#define ff first
#define ss second
#define vi vector<int>
#define vii vector<ii>
#define sz(a) (int)(a.size())
#define pb push_back
#define fto(i, a, b) for (int i = (int)(a); i <= (int)(b); ++i)
#define fdto(i, a, b) for (int i = (int)(a); i >= (int)(b); --i)
#define bug(x) "["#x" = "<<(x)<<"] "
#define maxN 2005

using namespace std;

const int MOD = oo;

int n, cs, cf;
ll f[maxN][maxN];

int main() {
    #ifndef EVAL
        freopen("CEOI16_kangaroo.INP", "r", stdin);
        freopen("CEOI16_kangaroo.OUT", "w", stdout);
    #endif

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

    cin >> n >> cs >> cf;

    f[1][1] = 1;
    fto(i, 2, n) {
        fto(j, 1, i) {
            if (i == cs || i == cf) {
                f[i][j] = (f[i-1][j-1] + f[i-1][j])%MOD;
            } else {
                f[i][j] = (f[i-1][j-1]*(j - (i > cs) - (i > cf))%MOD + f[i-1][j+1]*j%MOD)%MOD;
            }
        }
    }

    cout << f[n][1] << '\n';
    return 0;
}

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