ural 1225 Flags

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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:
Problem illustration

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
Tags: dynamic programming  (
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题意:蓝色只能在白红之间,不能连续放同一个颜色。问有几种方法
水题,简单DP。
#include <algorithm>#include <map>#include <cstring>#include <cmath>#include <iostream>using namespace std;#define lson l , m , rt << 1#define rson m + 1 , r , rt << 1 | 1#define LL __int64typedef long long ll;#define PI 3.1415926ll dp[46];int main(){     int i;     dp[1]=2;     dp[2]=2;     dp[3]=4;     for(i=4;i<=45;i++)        dp[i]=dp[i-1]+dp[i-2];     int n;     while(cin>>n)        cout<<dp[n]<<endl;     return 0;}

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