Ural 1225. Flags DP

1225. Flags

Time limit: 1.0 second
Memory limit: 64 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:

1. Stripes of the same color cannot be placed next to each other.
2. 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

inputoutput

3

4

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

其实算不上dp，只能算得上是递推

动态转移方程：f[i]=f[i-1]+f[i-2]

i表示i个布条，如果第i个为红或者白时，只需在前一个状态+1，如果第i个为蓝时，需要在i-2的状态加一个白或者红

注意数据类型！必须用long long 

#include<iostream>using namespace std;int main(){    int n;    long long f[50];    cin>>n;    f[1]=2;    f[2]=2;    for(int i=3; i<=n; i++)        f[i]=f[i-1]+f[i-2];    cout<<f[n]<<endl;    return 0;}