Submission #1188902

#	Time	Username	Problem	Language	Result	Execution time	Memory
1188902		AMnu	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	49 ms	55112 KiB

kangaroo

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define fi first
#define se second
typedef pair<ll,ll> pii;

const int MAXN = 2e3+5, MOD = 1e9+7;

int N, S, T;
ll dp[MAXN][MAXN][3];

int main(){
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    cin >> N >> S >> T;
    dp[1][1][S==1||T==1] = 1;
    for (int i=1;i<N;i++) {
        for (int j=1;j<=i;j++) {
            if (i+1==S || i+1==T) {
                for (int k=0;k<2;k++) {
                    dp[i+1][j+1][k+1] = (dp[i+1][j+1][k+1] + dp[i][j][k]) % MOD;
                    dp[i+1][j][k+1] = (dp[i+1][j][k+1] + dp[i][j][k]) % MOD;
                }
            }
            else {
                for (int k=0;k<3;k++) {
                    dp[i+1][j+1][k] = (dp[i+1][j+1][k] + dp[i][j][k]*(j+1-k)) % MOD;
                    // dp[i+1][j][k] = (dp[i+1][j][k] + dp[i][j][k]*(2*j-k)) % MOD;
                    dp[i+1][j-1][k] = (dp[i+1][j-1][k] + dp[i][j][k]*(j-1)) % MOD;
                }
            }
        }
    }
    cout << dp[N][1][2] << "\n";
}

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