Submission #307651

#	Time	Username	Problem	Language	Result	Execution time	Memory
307651		HynDuf	Kangaroo (CEOI16_kangaroo)	C++11	100 / 100	14 ms	512 KiB

kangaroo

#include <bits/stdc++.h>

#define task "K"
#define all(v) (v).begin(), (v).end()
#define rep(i, l, r) for (int i = (l); i <= (r); ++i)
#define Rep(i, r, l) for (int i = (r); i >= (l); --i)
#define DB(X) { cerr << #X << " = " << (X) << '\n'; }
#define DB1(A, _) { cerr << #A << "[" << _ << "] = " << (A[_]) << '\n'; }
#define DB2(A, _, __) { cerr << #A << "[" << _ << "][" << __ << "] = " << (A[_][__]) << '\n'; }
#define DB3(A, _, __, ___) { cerr << #A << "[" << _ << "][" << __ << "][" << ___ << "] = " << (A[_][__][___]) << '\n'; }
#define PR(A, l, r) { cerr << '\n'; rep(_, l, r) DB1(A, _); cerr << '\n';}
#define SZ(x) ((int)(x).size())
#define pb push_back
#define eb emplace_back
#define pf push_front
#define F first
#define S second
#define by(x) [](const auto& a, const auto& b) { return a.x < b.x; } // sort(arr, arr + N, by(a));
#define next ___next
#define prev ___prev
#define y1 ___y1
#define left ___left
#define right ___right
#define y0 ___y0
#define div ___div
#define j0 ___j0
#define jn ___jn

using ll = long long;
using ld = long double;
using ull = unsigned long long;
using namespace std;
typedef pair<int, int> ii;
typedef pair<ii, int> iii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<ll> vl;
const int N = 2002, mod = 1e9 + 7;
int n, dp[2][N], s, f;
int main()
{
#ifdef HynDuf
    freopen(task".in", "r", stdin);
    //freopen(task".out", "w", stdout);
#else
    ios_base::sync_with_stdio(false); cin.tie(nullptr);
#endif
    cin >> n >> s >> f;
    dp[1][1] = 1;
    rep(i, 2, n) rep(j, 0, n)
    {
        int now = i & 1, lst = now ^ 1;
        if (i == s || i == f) dp[now][j] = (dp[lst][j] + (j > 0 ? dp[lst][j - 1] : 0)) % mod;
        else dp[now][j] = (dp[lst][j + 1] * 1LL * j + (j > 0 ? dp[lst][j - 1] * 1LL * (j - (i > s) - (i > f)) : 0)) % mod;
    }
    cout << dp[n & 1][1];
    return 0;
}

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