Ural_Dynamic Programming Problems_1225-Flags

Description

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	output
3	4

Problem Source: 2002-2003 ACM Central Region of Russia Quarterfinal Programming Contest, Rybinsk, October 2002

Tags: dynamic programming (

hide tags for unsolved problems
)
Difficulty: 50

一道简单的递推题，当n=1时m=2，当n=2时m=2，当n=3时m=4，当n=4时m=6......可以推出当n>=3时a
=a[n-1]+a[n-2]，由此代码很容易就写出来了。

代码

#include <iostream>

using namespace std;

int main()
{
int n,i;
long long a[50];
a[1]=2;
a[2]=2;
for(i=3; i<50; i++)
a[i]=a[i-1]+a[i-2];
cin>>n;
cout<<a
<<endl;
return 0;
}