【杂谈】[scoi2006]整数划分

#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<algorithm>
#include<iostream>
using namespace std;
struct bign
{
int num[5000+10],len;
bign()
{
memset(num,0,sizeof(num));
len=1;
}
bign operator =(int x)
{
len=0;
while(x)
{
num[len++]=x%10;
x/=10;
}
if(len==0)len=1;
return *this;
}
bign operator =(const bign &b)
{
len=b.len;
for(int i=0;i<len;i++)num[i]=b.num[i];
return *this;
}
bign operator *(int x)
{
bign c;
c.len=len;
for(int i=0;i<len;i++)c.num[i]=num[i]*x;
int temp=0;
for(int i=0;i<c.len;i++)
{
c.num[i]+=temp;
temp=c.num[i]/10;
c.num[i]%=10;
if(i==c.len-1&&temp!=0)c.len++;
}
return c;
}
bign operator *(const bign &b)
{
bign c;
c.len=len+b.len-1;
for(int i=0;i<len;i++)
{
for(int j=0;j<b.len;j++)c.num[i+j]+=num[i]*b.num[j];
}
int temp=0;
for(int i=0;i<c.len;i++)
{
c.num[i]+=temp;
temp=c.num[i]/10;
c.num[i]%=10;
if(i==c.len-1&&temp!=0)c.len++;
}
return c;
}
void print()
{
printf("%d\n",len);
if(len<=100)
{
for(int i=len-1;i>=0;i--)printf("%d",num[i]);
printf("\n");
}
else
{
for(int i=len-1;i>=len-100;i--)printf("%d",num[i]);
printf("\n");
}
}
};
int n;
bign qpow(int d,int c)
{
bign ret;
if(c==0)return ret=1;
if(c==1)return ret=d;
ret=qpow(d,c/2);
ret=ret*ret;
if(c&1)ret=ret*d;
return ret;
}
int main()
{
scanf("%d",&n);
int r=n/3;
if(n%3==1)r--;
int s=n-r*3;
bign ans;
ans=qpow(3,r);
if(s)ans=ans*s;
ans.print();
return 0;
}