Submission #735816

#	Time	Username	Problem	Language	Result	Execution time	Memory
735816		danikoynov	Kangaroo (CEOI16_kangaroo)	C++14	100 / 100	38 ms	31640 KiB

kangaroo

/**
 ____ ____ ____ ____ ____ ____
||l |||e |||i |||n |||a |||d ||
||__|||__|||__|||__|||__|||__||
|/__\|/__\|/__\|/__\|/__\|/__\|

**/

#include<bits/stdc++.h>
#define endl '\n'

using namespace std;
typedef long long ll;

void speed()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
}

const int maxn = 2010;
const ll mod = 1e9 + 7;
int n, s, f;
ll dp[maxn][maxn];

void add(ll &cell, ll val)
{
    cell += val;
    if (cell >= mod)
        cell -= mod;
}

void solve()
{
    cin >> n >> s >> f;
    if (s > f)
        swap(s, f);

    dp[1][1] = 1;
    for (int i = 2; i <= n; i ++)
    {
        for (int j = 1; j <= n; j ++)
        if (i == s || i == f)
        {
            add(dp[i][j], dp[i - 1][j]);
            add(dp[i][j], dp[i - 1][j - 1]);
        }
        else
        {
            ll ways = (dp[i - 1][j + 1] * j) % mod;
            add(dp[i][j], ways);
            ways = (dp[i - 1][j - 1] * (j - (s < i) - (f < i))) % mod;
            add(dp[i][j], ways);
        }
    }

    cout << dp[n][1] << endl;

}

int main()
{
    solve();
    return 0;
}

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