/*a[i]代表最后一位为o，b[i]代表最后一位不为o,x[i]为全部的字符串个数
x[i] = a[i] +
b[i];
a[i] = b[i-1];
b[i] = x[i-1]*2;
x[i] =
a[i]+b[i] = b[i-1]+x[i-1]*2 = x[i-2]*2 +
x[i-1]*2;
*/
#include<stdio.h>
#include<string.h>
__int64
x[45];
int main()
{
int
i,j,n;
memset(x,0,sizeof(x));
x[1] = 3;
x[2] = 8;
while(scanf("%d",&n) != EOF)
{
if(x[n] ==
0)
{
for(i = 2;x[i] !=
0;i++);
for(j = i;j <= n;j++)
{
x[j] = x[j-1]*2 +
x[j-2]*2;
}
}
printf("%I64d\n",x[n]);
}
return 0;
}
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原文：http://www.cnblogs.com/flying123/p/3601240.html