Submission #538370

#	Time	Username	Problem	Language	Result	Execution time	Memory
538370		alextodoran	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	27 ms	15948 KiB

kangaroo

/**
 ____ ____ ____ ____ ____
||a |||t |||o |||d |||o ||
||__|||__|||__|||__|||__||
|/__\|/__\|/__\|/__\|/__\|

**/

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int N_MAX = 2000;
const int MOD = (int) 1e9 + 7;

int N, L, R;

int dp[N_MAX + 2][N_MAX + 2];

int main () {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    cin >> N >> L >> R;

    dp[0][1] = 1;
    for (int i = 1; i <= N; i++) {
        for (int open = 0; open <= N; open++) {
            if (i == L || i == R) {
                dp[i][open] += dp[i - 1][open];
                if (dp[i][open] >= MOD) {
                    dp[i][open] -= MOD;
                }
                dp[i][open - 1] += dp[i - 1][open];
                if (dp[i][open - 1] >= MOD) {
                    dp[i][open - 1] -= MOD;
                }
            } else {
                dp[i][open + 1] = (dp[i][open + 1] + (ll) dp[i - 1][open] * open) % MOD;
                dp[i][open - 1] = (dp[i][open - 1] + (ll) dp[i - 1][open] * max(0, open - (i < L) - (i < R))) % MOD;
            }
        }
    }

    cout << dp[N][0] << "\n";

    return 0;
}

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