Submission #1118231

#	Time	Username	Problem	Language	Result	Execution time	Memory
1118231		vjudge1	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	38 ms	31836 KiB

kangaroo

#pragma GCC optimize("-O3")
#include<bits/stdc++.h>
#define ll long long
#define ld long double
#define vl vector<ll>
#define vi vector<int>
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define pb push_back
#define sz(v) (ll)(v.size())
#define f first
#define s second
#define pii pair<int, int>
#define pll pair<ll, ll>
using namespace std;
const ll mod = 1e9+7;
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    ll n, cs, cf, i, j, c = 0;
    cin >> n >> cs >> cf;
    ll dp[n+5][n+5];
    for(i = 0; i <= n; i++)
    {
        for(j = 0; j <= n; j++)
            dp[i][j] = 0;
    }
    dp[1][1] = 1;
    for(i = 1; i <= n; i++)
    {
        if(i == cs || i == cf)
            c++;
        for(j = 1; j < i; j++)
        {
            if(i == cs || i == cf)
            {
                dp[i][j] += dp[i-1][j];
                dp[i][j+1] += dp[i-1][j];
                dp[i][j] %= mod;
                dp[i][j+1] %= mod;
            }
            else
            {
                dp[i][j-1] += dp[i-1][j] * (j-1);
                dp[i][j+1] += dp[i-1][j] * (j + 1 - c);
                dp[i][j-1] %= mod;
                dp[i][j+1] %= mod;
            }
        }
    }
    cout << dp[n][1] % mod << "\n";
}

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