Submission #900625

#	Time	Username	Problem	Language	Result	Execution time	Memory
900625		warner1129	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	33 ms	488 KiB

kangaroo

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

 
#ifdef LOCAL
template<class... T> void dbg(T... x) { char e{}; ((cerr << e << x, e = ' '), ...); }
#define debug(x...) dbg(#x, '=', x, '\n')
#else
#define debug(...) ((void)0)
#endif
 
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define ff first
#define ss second
 
using u32 = unsigned int;
using i64 = long long;
using u64 = unsigned long long;
using i128 = __int128;
using u128 = unsigned __int128;
 
template<class T> inline constexpr T inf = numeric_limits<T>::max() / 2;
constexpr int mod = 1e9 + 7, inv2 = (mod + 1) / 2;
 
template<class T> bool chmin(T &a, T b) { return (b < a and (a = b, true)); }
template<class T> bool chmax(T &a, T b) { return (a < b and (a = b, true)); }

void solve() {
    int n, s, t;
    cin >> n >> s >> t;

    int op = s > 1;
    int ed = t > 1;
    vector dp(n + 1, array<i64, 3>{});
    
    dp[1][0] = 1;
    
    for (int i = 2; i <= n; i++) {
        decltype(dp) f(n + 1, array<i64, 3>{});
        
        for (int j = 1; j < i; j++) {
            if (i == s or i == t) {
                f[j][1] += dp[j][0];
                f[j][2] += dp[j][1];
                f[j + 1][0] += dp[j][0];
                f[j + 1][1] += dp[j][1];
                f[j + 1][2] += dp[j][2];
            } else {
                for (int x : {0, 1, 2}) {
                    f[j - 1][x] += dp[j][x] * (j - 1);
                    f[j + 1][x] += dp[j][x] * (i - 1 - j + op + ed - x);
                }
            }
        }

        if (s == i) op = 0;
        if (t == i) ed = 0;
        
        dp.swap(f);
        for (auto &x : dp)
            for (auto &v : x) v %= mod;
    }

    cout << (dp[1][0] + dp[1][1] + dp[1][2]) % mod << '\n';
}
 
signed main() {
    cin.tie(0)->sync_with_stdio(false);
    cin.exceptions(cin.failbit);
    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