4103:踩方格

 1 #include<iostream>
 2 #include<cstdio>
 3 using namespace std;
 4 int n,ans;
 5 int l[30],r[30],u[30];
 6 int main()
 7 {
 8     cin>>n;
 9     if (n==1) cout<<3;
10       else
11        { 
12           l[1]=1;
13           r[1]=1;
14           u[1]=1;
15           for (int i=2;i<=n;i++)
16             {
17               l[i]=l[i-1]+u[i-1];
18               r[i]=r[i-1]+u[i-1];
19               u[i]=l[i-1]+r[i-1]+u[i-1];
20             }
21           ans=l[n]+r[n]+u[n];
22           cout<<ans<<endl;
23        }
24     return 0;
25 }