Submission #587231

#	Time	Username	Problem	Language	Result	Execution time	Memory
587231		Jarif_Rahman	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	31 ms	31712 KiB

kangaroo

#include <bits/stdc++.h>
#define pb push_back
#define f first
#define sc second
using namespace std;
typedef long long int ll;
typedef string str;

const ll md = 1e9+7;

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

    int n, s, e; cin >> n >> s >> e; s--, e--;

    vector<vector<ll>> dp(n, vector<ll>(n+1, 0));
    dp[0][1] = 1;

    for(int i = 1; i < n; i++) for(int j = 1; j <= i+1; j++) {
        int c = 0;
        c+=(s < i);
        c+=(e < i);

        if(j > 1) dp[i][j]+=dp[i-1][j-1], dp[i][j]%=md;

        if(i == s || i == e){
            if(c == 0) dp[i][j]+=(dp[i-1][j]*j)%md, dp[i][j]%=md;
            else if(i == n-1 && j == 1) dp[i][j]+=dp[i-1][j], dp[i][j]%=md;
            else if(j != 1) dp[i][j]+=(dp[i-1][j]*(j-1))%md, dp[i][j]%=md;
        }
        else if(j+1 <= i){
            if(c == 0) dp[i][j]+=(dp[i-1][j+1]*j*(j+1))%md, dp[i][j]%=md;
            else if(c == 1) dp[i][j]+=(dp[i-1][j+1]*j*j)%md, dp[i][j]%=md;
            else if(i == n-1 && j == 1) dp[i][j]+=dp[i-1][j+1], dp[i][j]%=md;
            else if(j != 1) dp[i][j]+=(dp[i-1][j+1]*j*(j-1))%md, dp[i][j]%=md;
        }
    }

    cout << dp[n-1][1] << "\n";
}

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