Submission #1193902

#	Time	Username	Problem	Language	Result	Execution time	Memory
1193902		Ghulam_Junaid	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	50 ms	55112 KiB

kangaroo

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;

const int N = 2005, mod = 1e9 + 7;
int n, st, en;
ll dp[N][N][3];

int main(){
    cin >> n >> st >> en;
    dp[1][1][(st == 1) + (en == 1)] = 1;
    for (int i = 1; i < n; i ++){
        for (int j = 1; j <= i; j ++){
            if (i + 1 == st or i + 1 == en){
                for (int k = 0; k < 2; k ++){
                    dp[i + 1][j][k + 1] += dp[i][j][k];
                    dp[i + 1][j][k + 1] %= mod;
                    dp[i + 1][j + 1][k + 1] += dp[i][j][k];
                    dp[i + 1][j + 1][k + 1] %= mod;
                }
                continue;
            }

            for (int k = 0; k < 3; k ++){
                dp[i + 1][j + 1][k] += dp[i][j][k] * (j + 1 - k);
                dp[i + 1][j + 1][k] %= mod;
                dp[i + 1][j - 1][k] += dp[i][j][k] * (j - 1);
                dp[i + 1][j - 1][k] %= mod;
            }
        }
    }
    cout << dp[n][1][2] << endl;
}

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