Submission #1123837

#	Time	Username	Problem	Language	Result	Execution time	Memory
1123837		ljtunas	Kangaroo (CEOI16_kangaroo)	C++20	Running #3-3	66 ms	98444 KiB

kangaroo

// author : anhtun_hi , nqg
#include <bits/stdc++.h>
#define ll long long
#define ii pair<ll, ll>
#define fi first
#define se second
#define all(x) x.begin(), x.end()
#define reset(h, v)    memset(h, v, sizeof h)
#define Forv(i, a)     for(auto& i : a)
#define For(i, a, b)   for(int i = a; i <= b; ++i)
#define Ford(i, a, b)  for(int i = a; i >= b; --i)
#define c_bit(i)     __builtin_popcountll(i)
#define Bit(mask, i)    ((mask >> i) & 1LL)
#define onbit(mask, i)  ((mask) bitor (1LL << i))
#define offbit(mask, i) ((mask) &~ (1LL << i))
#define Log2(x) (63 - __builtin_clzll(x))
#define TIME (1.0 * clock() / CLOCKS_PER_SEC)
using namespace std;
namespace std {
    template <typename T, int D>
    struct _vector : public vector <_vector <T, D - 1>> {
        static_assert(D >= 1, "Dimension must be positive!");
        template <typename... Args>
        _vector(int n = 0, Args... args) : vector <_vector <T, D - 1>> (n, _vector <T, D - 1> (args...)) {}
    };
    template <typename T> struct _vector <T, 1> : public vector <T> {
        _vector(int n = 0, const T& val = T()) : vector <T> (n, val) {}
    };
    template <class A, class B> bool minimize(A &a, B b){return a > b ? a = b, true : false;}
    template <class A, class B> bool maximize(A &a, B b){return a < b ? a = b, true : false;}
}
const int dx[] = {0, 0, +1, -1}, dy[] = {-1, +1, 0, 0}, LOG = 20, base = 311, inf = 1e9 + 5;
const int MAXN = 5e3 + 5;
const  ll  mod = 1e9 + 7;
const  ll   oo = 1e18;

//#define int long long

namespace Mod{

    inline void add(int &x, const int &y) { if((x += y) >= mod) x -= mod; }

    inline void sub(int &x, const int &y) { if((x -= y) < 0) x += mod; }

    inline void Mul(int &x, const int &y) { x = 1LL * x * y % mod; }

    inline int mul(const int &x, const int &y) { return 1LL * x * y % mod; }

    inline int sum(const int &x, const int &y) { int res = x + y; if(res >= mod) res -= mod; return res; }

    inline int diff(const int &x, const int &y) { int res = x - y; if(res < 0) res += mod; return res; }

} using namespace Mod;

int n, s, t, dp[MAXN][MAXN];

int solve(int i, int j)
{
    if (j < 0) return 0;
    if (i > n) return j == 1;
    if (~dp[i][j]) return dp[i][j];
    int res = 0, cost = (i > s) + (i > t);
    if (i == s || i == t) {
        add(res, solve(i + 1, j + 1));
        add(res, solve(i + 1, j));
    } else {
        add(res, solve(i + 1, j + 1) * (j + 1 - cost));
        add(res, solve(i + 1, j - 1) * (j - 1));
    }
    return dp[i][j] = res;
}

void Solve() {
    cin >> n >> s >> t;
    memset(dp, -1, sizeof dp);
    if (n == 2) cout << 1 << '\n';
    else cout << solve(1, 0) << '\n';
}

signed main() {
    cin.tie(0) -> sync_with_stdio(0);
    if(fopen("kangaroo.inp", "r")) {
        freopen("kangaroo.inp", "r", stdin);
        freopen("kangaroo.out", "w", stdout);
    }

    int t = 1;
//    cin >> t;
    while(t --) Solve();

    return 0;
}

Compilation message (stderr)

kangaroo.cpp: In function 'int main()':
kangaroo.cpp:83:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   83 |         freopen("kangaroo.inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
kangaroo.cpp:84:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   84 |         freopen("kangaroo.out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 6 / 6
• Subtask 2: 0 / 30
• Subtask 3: 0 / 15