Flags-Ural1225简单递推
Time limit: 1.0 second | Memory limit: 64 MB |
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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:
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
input
3
output
4
Problem Source:
2002-2003 ACM Central Region of Russia Quarterfinal Programming Contest, Rybinsk, October 2002
简单的递推,三种颜色的布,相邻的颜色不能相同,蓝色在红色与白色之间,则用1表示红色,2表示白色,Dp[i][j]表示第i个条纹的颜色为j是的状态数目,当j=1时,如果i-1的颜色为白色,则Dp[i][1]+=Dp[i-1][2],如果为蓝色,则取决于i-2的颜色为白色状态,所以Dp[i][1]=Dp[i-1][2]+Dp[i-2][2],则Dp[i][2]=Dp[i-1][1]+Dp[i-2][1].
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <string>
#include <queue>
#include <vector>
#include <deque>
#include <iostream>
#include <algorithm>
using namespace std;
long long Dp[50][3];
int main()
{
memset(Dp,0,sizeof(Dp));
Dp[1][1]=Dp[1][2]=1;
for(int i=2;i<=45;i++)
{
Dp[i][1] =Dp[i-1][2]+Dp[i-2][2];
Dp[i][2] = Dp[i-1][1]+Dp[i-2][1];
}
int n;
while(~scanf("%d",&n))
{
cout<<Dp[n][1]+Dp[n][2]<<endl;
}
return 0;
}