Submission #1294241

#	Time	Username	Problem	Language	Result	Execution time	Memory
1294241		okahak71	Kangaroo (CEOI16_kangaroo)	C++20	100 / 100	23 ms	31856 KiB

kangaroo

#include <bits/stdc++.h>
#define ll long long
#define vec vector
#define pb push_back
#define pll array<ll, 2>
#define all(X) X.begin(), X.end()
#define allr(X) X.rbegin(), X.rend()
using namespace std;

const ll inf = 1e18;
const ll mod = 1e9 + 7;

void _(){
    ll n, cs,cf; cin >> n >> cs >> cf;
    vec<vec<ll>>dp(n + 1, vec<ll>(n + 1, 0));
    dp[1][1] = 1; ll fx = 0;
    for(ll i = 1; i <= n; i++){
        if(i == cs or i == cf) fx++;
        for(ll j = 1; j <= i; j++){
            if(i == cs or i == cf){
                (dp[i][j + 1] += dp[i - 1][j]) %= mod;
                (dp[i][j] += dp[i - 1][j]) %= mod;
            }
            else{
                (dp[i][j + 1] += (j + 1 - fx) * dp[i - 1][j]) %= mod;
                (dp[i][j - 1] += (j - 1) * dp[i - 1][j]) %= mod;
            }
        }
    } cout << dp[n][1] << endl;
}

signed main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0); _();
}

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