Submission #839189

#	Time	Username	Problem	Language	Result	Execution time	Memory
839189		guagua0407	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	20 ms	23092 KiB

kangaroo

//#pragma GCC optimize("O3")
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pii pair<int,int>
#define f first
#define s second
#define all(x) x.begin(),x.end()
#define _ ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);

void setIO(string s) {
    freopen((s + ".in").c_str(), "r", stdin);
    freopen((s + ".out").c_str(), "w", stdout);
}

const int mxn=2005;
const int mod=1e9+7;
ll dp[mxn][mxn];
int cnt=0;

int main() {_
    int n,st,en;
    cin>>n>>st>>en;
    if(st>en) swap(st,en);
    dp[1][1]=1;
    if(1==st) cnt++;
    for(int i=1;i<n;i++){
        if(i+1==st){
            // new
            for(int j=1;j<=i;j++){
                dp[i+1][j+1]=(dp[i+1][j+1]+dp[i][j])%mod;
            }
            // continue
            for(int j=1;j<=i;j++){
                dp[i+1][j]=(dp[i+1][j]+dp[i][j]*j)%mod;
            }
            cnt++;
        }
        else if(i+1==en){
            // new
            for(int j=1;j<=i;j++){
                dp[i+1][j+1]=(dp[i+1][j+1]+dp[i][j])%mod;
            }
            // continue
            for(int j=1;j<=i;j++){
                dp[i+1][j]=(dp[i+1][j]+dp[i][j]*(j-1+(i==n-1 and j==1)))%mod;
            }
            cnt++;
        }
        else{
            // new
            for(int j=1;j<=i;j++){
                dp[i+1][j+1]=(dp[i+1][j+1]+dp[i][j])%mod;
            }
            // combine
            for(int j=1;j<=i;j++){
                dp[i+1][j-1]=(dp[i+1][j-1]+dp[i][j]*(j*(j-1)-(j-1)*cnt+(cnt==2 and i==n-1)))%mod;
            }
        }
    }
    cout<<dp[n][1]<<'\n';
    return 0;
}
//maybe its multiset not set

Compilation message (stderr)

kangaroo.cpp: In function 'void setIO(std::string)':
kangaroo.cpp:12:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   12 |     freopen((s + ".in").c_str(), "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
kangaroo.cpp:13:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   13 |     freopen((s + ".out").c_str(), "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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