Timus 1225. Flags dp

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1225. Flags
Time Limit: 1.0 second
Memory Limit: 16 MB
On the Day of the Flag of Russia a shop-owner decided to decorate the show-window of his shop with textile stripes of white, blue and red colors. He wants to satisfy the following conditions:
Stripes of the same color cannot be placed next to each other.
A blue stripe must always be placed between a white and a red or between a red and a white one.
Determine the number of the ways to fulfill his wish.
Example. For N = 3 result is following:

Input
N, the number of the stripes, 1 ≤ N ≤ 45.
Output
M, the number of the ways to decorate the shop-window.
Sample

input
3

output

#include<iostream> #include<fstream> using namespace std; int main() { int n; cin>>n; long long a[50][3]; a[1][0]=1; //white a[1][1]=0;//blue a[1][2]=1;//red a[2][0]=1; a[2][1]=0; a[2][2]=1; for(int i=3;i<=n;i++) { if( i<n) { a[i][0]=a[i-1][2]+a[i-2][2]; a[i][1]=a[i][1]+a[i][2]; a[i][2]=a[i-1][0]+a[i-2][0]; } else { a[i][0]=a[i-1][2]+a[i-2][2]; a[i][2]=a[i-1][0]+a[i-2][0]; } } cout<<a[n][0]+a[n][2]<<endl; }

discuss里有人这么说：

use fibonacci
1,1,2,3,5,8,13...

answer = fibonacci(3)*2;

不明白……但这么做答案是对的。

我用的是dp