bzoj1002

题解：

f[i]=(f[i-1]*3+f[i-2]);

高精度计算

代码：

#include<bits/stdc++.h>
using namespace std;
struct big
{
    int a[],len;
};
int n;
big cf(big a,int k)
{
    for (int i=;i<=a.len;i++)a.a[i]*=k;
    for (int i=;i<=a.len;i++)
     {
        a.a[i+]+=a.a[i]/;
        a.a[i]%=;
     }
    if (a.a[a.len+]!=)a.len++;
    return a;
}
big jf(big a,big b)
{
    a.a[]+=;
    int j=;
    while (a.a[j]>=){a.a[j]%=;a.a[j+]++;j++;}
    for (int i=;i<=a.len;i++)
     {
        a.a[i]-=b.a[i];
        if(a.a[i]<){a.a[i]+=;a.a[i+]--;}
     }
    while (a.a[a.len]==)a.len--;
    return a;
}
int main()
{
    big f[];f[].a[]=;f[].a[]=;
    f[].len=f[].len=;
    scanf("%d",&n);
    for (int i=;i<=n;i++)f[i]=jf(cf(f[i-],),f[i-]);
    for (int i=f[n].len;i;i--)printf("%d",f[n].a[i]);
    return ;
}