Submission #770377

#	Time	Username	Problem	Language	Result	Execution time	Memory
770377		Sami_Massah	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	138 ms	126332 KiB

kangaroo

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


const int maxn = 2000 + 12, mod = 1e9 + 7;
long long n, s, e, dp[maxn][maxn][4];
int main(){
    cin >> n >> s >> e;
    if(1 == s){
        dp[1][1][1] = 1;
    }
    else if(e == 1){
        dp[1][1][2] = 1;
    }
    else{
        dp[1][1][0] = 1;
    }
    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= n; j++)
            for(int c = 0; c < 4; c++){
              //  cout << i << ' ' << j << ' ' << c << ' ' << dp[i][j][c] << endl;
                dp[i][j][c] %= mod;
                if(i + 1 == s){
                    dp[i + 1][j][c | 1] += dp[i][j][c];
                    dp[i + 1][j + 1][c | 1] += dp[i][j][c];
                }
                else if(i + 1 == e){
                    dp[i + 1][j][c | 2] += dp[i][j][c];
                    dp[i + 1][j + 1][c | 2] += dp[i][j][c];
                }
                else{
                    int cnt = j + 1;
                    if(c & 2)
                        cnt -= 1;
                    if(c & 1)
                        cnt -= 1;
                    dp[i + 1][j + 1][c] += dp[i][j][c] * cnt % mod;
                    dp[i + 1][j - 1][c] += dp[i][j][c] * (j - 1) % mod;

                }

            }
    //    cout << endl;
    }
    cout << dp[n][1][3] % mod << endl;
}

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