Submission #316932

#	Time	Username	Problem	Language	Result	Execution time	Memory
316932		Kuuhaku	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	91 ms	14200 KiB

kangaroo

#define tasknames "Kangaroo"
#include <iostream>
#include <stdio.h>
using namespace std;
const int maxn=2e3+2;
int n, cs, cf, dp[maxn][maxn], mod=1e9+7;

void Enter()
{
    cin>>n>>cs>>cf;
    if(cs>cf)swap(cs,cf);
    dp[1][0]=1;
    for(int i=1;i<=n;i++)
        for(int j=0;j<=i;j++)
        {
            if(i==cs||i==cf)
            {
                dp[i+1][j]=(dp[i+1][j]+dp[i][j])%mod;
                if(j)dp[i+1][j-1]=(dp[i+1][j-1]+1ll*j*dp[i][j]%mod)%mod;
            }
            else
            {
                if(i>cf)
                    dp[i+1][j-1]=(dp[i+1][j-1]+1ll*j*dp[i][j]%mod)%mod;
                if(i>cs)
                    dp[i+1][j-1]=(dp[i+1][j-1]+1ll*j*dp[i][j]%mod)%mod;
                dp[i+1][j+1]=(dp[i+1][j+1]+dp[i][j])%mod;
                dp[i+1][j-1]=(dp[i+1][j-1]+1ll*j*(j-1)*dp[i][j]%mod)%mod;
            }
        }
    cout<<dp[n][0];
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    if(fopen(tasknames".INP","r"))
    {
    	freopen(tasknames".INP","r",stdin);
        freopen(tasknames".OUT","w",stdout);
    }
    Enter();
}

Compilation message (stderr)

kangaroo.cpp: In function 'int main()':
kangaroo.cpp:40:13: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
   40 |      freopen(tasknames".INP","r",stdin);
      |      ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
kangaroo.cpp:41:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
   41 |         freopen(tasknames".OUT","w",stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~

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