제출 #671259

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
671259		uylulu	캥거루 (CEOI16_kangaroo)	C++17	0 / 100	46 ms	125644 KiB

kangaroo

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

#define ld long double
#define int long long
#define endl "\n"

const int N = 2000,mod = 1e9 + 7;

int dp[N + 1][N + 1][2][2],n,a,b;

int f(int pos,int comp,bool front,bool back) {
    if(comp < 0) return 0; 

    if(pos == n + 1) {
        return comp == 1;
    }
    if(dp[pos][comp][front][back] != -1) return dp[pos][comp][front][back];

    if(pos == a) {
        int res = 0;

        res = (res + f(pos + 1,comp + 1,0,back))%mod;
        if(!front) {
            res = (res + f(pos + 1,comp,1,back))%mod;
        }
        return dp[pos][comp][front][back] = res;
    }
    if(pos == b) {
        int res = 0;

        res = (res + f(pos + 1,comp + 1,front,0))%mod;
        if(!back) {
            res = (res + f(pos + 1,comp,front,1))%mod;
        }
        return dp[pos][comp][front][back] = res;
    }

    int res = 0;
    if(!front && pos < a) {
        res = (res + f(pos + 1,comp,1,back))%mod;
    }
    if(pos < a) {
        res = (res + f(pos + 1,comp + 1,0,back))%mod;
    }
    if(!back && pos < b) {
        res = (res + f(pos + 1,comp,front,1))%mod;
    }
    if(pos < b) {
        res = (res + f(pos + 1,comp + 1,front,0))%mod;
    }
    res = (res + (f(pos + 1,comp + 1,front,back) * (comp - 1))%mod)%mod;
    res = (res + (f(pos + 1,comp - 1,front,back) * (comp - 1))%mod)%mod;
    return dp[pos][comp][front][back] = res;
}
 
signed main() {
    ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    // freopen("in.txt","r",stdin);
    // freopen("out.txt","w",stdout);

    cin>>n>>a>>b;
    memset(dp,-1,sizeof(dp));
    cout<<f(2,1,0,0)<<endl;

    return 0;
}   

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