Submission #488126

#	Time	Username	Problem	Language	Result	Execution time	Memory
488126		DrearyJoke	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	30 ms	31692 KiB

kangaroo

#include<bits/stdc++.h>

using namespace std;

using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

#define ff first
#define ss second
#define pb push_back
#define mp make_pair
#define END "\n"
#define rall(v) (v).rbegin(), (v).rend()
#define all(v) (v).begin(), (v).end()
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#include <ext/pb_ds/assoc_container.hpp>

using namespace __gnu_pbds;
template <typename T>
using ordered_set =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

constexpr ll modu = 1e9 + 7;

void solve(){
    int n, a, b;
    cin >> n >> a >> b;
    if (a > b) swap(a, b);
    vector<vector<ll>> dp(n + 1, vector<ll>(n + 2));
    dp[0][0] = 1;
    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j <= n; ++j) {
            if (i == a || i == b) dp[i][j] += dp[i - 1][j - 1] + dp[i - 1][j];
            else {
                if (i < a && i < b) {
                    dp[i][j] += (j * (dp[i - 1][j + 1] + dp[i - 1][j - 1]));
                } else if (i > a && i < b) {
                    dp[i][j] += (j - 1) * (dp[i - 1][j + 1] + dp[i - 1][j - 1]) + dp[i - 1][j + 1];
                } else {
                    dp[i][j] += (j - 2) * (dp[i - 1][j + 1] + dp[i - 1][j - 1]) + 2 * dp[i - 1][j + 1];
                }
            }
            dp[i][j] %= modu;
        }
    }
    cout << dp[n][1] << END;
}
int main()
{
    fastio
    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