Submission #551857

#	Time	Username	Problem	Language	Result	Execution time	Memory
551857		leaked	Kangaroo (CEOI16_kangaroo)	C++17	0 / 100	1 ms	340 KiB

kangaroo

#include <bits/stdc++.h>

#define f first
#define s second
#define m_p make_pair
#define vec vector
#define pb push_back
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define pw(x) (1LL<<(x))
#define sz(x) (int)(x).size()

using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const int M=1e9+7;
void add(int &a,int b){
    a+=b;
    if(a>=M) a-=M;
    else if(a<0) a+=M;
}
int mult(int a,int b){
    return 1ll*a*b%M;
}
const int N=2e3+1;
int dp[N][N];
/// len,pos and last was left/right
signed main(){
    ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    int n,x,y;
    cin>>n>>x>>y;--x;--y;
    dp[1][1]=1;
//    dp[1][1]=1;
    for(int i=1;i<n;i++){
        for(int c=0;c<=i;c++){
            if(i==x || i==y){
                /// if i just in beginning
                add(dp[i+1][c],dp[i][c]);
                add(dp[i+1][c+1],dp[i][c]);
            }
            else{
//                /// if i choose between them
//                int cnt=(i-1)-(c-1);
//
//                add(dp[i+1][c],mult(dp[i][c],cnt));

                /// if i make new comp
                int w=c-(i>=x)-(i>=y);
                add(dp[i+1][c+1],mult(dp[i][c],w));

                if(c)
                    add(dp[i+1][c-1],mult(dp[i][c],c-1));
            }
//            cout<<dp[i][c]<<' ';
        }
//        cout<<endl;
    }
    cout<<dp[n][1];
    return 0;
}
/*
5 14
3 7 1 5 10
1 3 5 7 10
11 2
aa
ab
aa
ca
aa
bc
ea
aa
ad
de
aa


*/

• Subtask 1: 0 / 6
• Subtask 2: 0 / 30
• Subtask 3: 0 / 15
• Subtask 4: 0 / 49