Submission #1322752

#TimeUsernameProblemLanguageResultExecution timeMemory
1322752bluocarootKangaroo (CEOI16_kangaroo)C++20
100 / 100
59 ms28192 KiB
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using ll = long long;
using namespace std;
using namespace __gnu_pbds;
template<typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
const double pi = acos(-1);
const int N = 2e3 + 5, K = 1e3 + 5, SQ = 500, M = 1e9 + 7;
//#define TESTS
//#define INTERACTIVE
//#define COMMUNICATION

/*
 * Remember who you are.
 */

void pre() {

}
int dp[N][N], vis[N][N], vid, n, s, e;
int rec(int i, int j)
{
    if (j < 0)
        return 0;
    if (i == n)
        return j == 1;
    auto &ret = dp[i][j], &v = vis[i][j];
    if (v == vid)
        return ret;
    v = vid;
    ret = 0;
    if (s == i || e == i)
        ret = rec(i + 1, j + 1) + rec(i + 1, j);
    else
        ret = 1ll * rec(i + 1, j + 1) * (j + 1 - (i > s) - (i > e)) % M
                +
                1ll * rec(i + 1, j - 1) * (j - 1) % M;
    return ret %= M;
}
void solve() {
    cin >> n >> s >> e;
    s--, e--;
    ++vid;
    cout << rec(0, 0);

}


void solve2() {

}

signed main() {
    ios::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
#ifdef CAROOT
#ifndef INTERACTIVE
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
#else
#endif
    int tt = 1;
    pre();
#ifdef COMMUNICATION
    string run;
    cin >> run;
#endif
#ifdef TESTS
    cin >> tt;
#endif
    for (int tc = 1; tc <= tt; ++tc) {
#ifdef COMMUNICATION
        if (run == "first")
            solve();
        else
            solve2();
#else
        solve();
#endif
        cout << '\n';
    }
}
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