Submission #704541

#	Time	Username	Problem	Language	Result	Execution time	Memory
704541		ByeWorld	Kangaroo (CEOI16_kangaroo)	C++14	100 / 100	143 ms	133652 KiB

kangaroo

#include <bits/stdc++.h>
#pragma GCC optimize("O1")
#define int long long
#define fi first
#define se second
#define pb push_back
#define lb lower_bound
#define ub upper_bound
using namespace std;
const int MAXN = 3e3+10;
const double SMALL = 1e-6;
const int INF = 5e5+10;
const int MX = 2e12;
const int MOD = 1e9+7;
typedef pair<int,int> pii;
typedef pair<pii,int> ipii;
int sum(int a, int b){
    return (a+b)%MOD;
}
int mul(int a, int b){
    return (a*b)%MOD;
}

int dp[MAXN][MAXN][4]; // dp[id][cc]

signed main(){
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    int n, S, T; cin >> n >> S >> T;
    dp[0][0][0] = 1;
    for(int i=1; i<=n; i++){
        for(int j=1; j<=n; j++){
            if(i==S || i==T){
                for(int k=0; k<=1; k++){
                    dp[i][j][k+1] = sum(dp[i-1][j-1][k], dp[i][j][k+1]);
                    dp[i][j][k+1] = sum(dp[i-1][j][k], dp[i][j][k+1]);
                }
                continue;
            }
            for(int k=0; k<=2; k++){
                dp[i][j][k] = sum(mul(dp[i-1][j-1][k], j-k), dp[i][j][k]);
                //dp[i][j][k] = sum(mul(dp[i-1][j][k], mul(2, j)-k), dp[i][j][k]);
                dp[i][j][k] = sum(mul(dp[i-1][j+1][k], j), dp[i][j][k]);
            }
        }
    }
    cout << dp[n][1][2]+dp[n][1][1]+dp[n][1][0] << '\n';
    //cout << dp[n][1][2] << ' ' << dp[n][1][1] << ' ' <<dp[n][1][0] << '\n';
}

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