自己用手算一下可以发现是斐波那契数列,然后因为数字很大,用高精度
以后做题的时候记得算几个数据找规律
#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
#define REP(i, a, b) for(int i = (a); i < (b); i++)
using namespace std;
const int MAXN = 11234;
const int MAXM = 2500;
struct node
{
int len, d[MAXM];
node() { len = 0; memset(d, 0, sizeof(d)); };
}f[MAXN];
node add(node a, node b)
{
node c;
c.len = max(a.len, b.len);
REP(i, 0, c.len)
{
c.d[i] += a.d[i] + b.d[i];
if(c.d[i] >= 10) c.d[i] -= 10, c.d[i+1]++;
}
if(c.d[c.len] > 0) c.len++;
return c;
}
void init()
{
f[3].d[0] = 4; f[3].len = 1;
f[4].d[0] = 7; f[4].len = 1;
REP(i, 5, MAXN) f[i] = add(f[i-1], f[i-2]);
}
void print(node c)
{
for(int i = c.len - 1; i >= 0; i--)
printf("%d", c.d[i]);
puts("");
}
int main()
{
init();
int n;
while(~scanf("%d", &n))
print(f[n]);
return 0;
}