UVA10236 斐波那契素数

题意：任取斐波那契数列中一项f[i],若对于所有j
解法：这题的理论分析在黑书上有，结论是从第五项开始下标为素数的斐波那契数都是斐波那契素数

#include <stdio.h>
#include <string.h>
const int MAXN = 250010;;
int prime[25010];
bool isprime[MAXN];
long double fib[MAXN];
int main(){int i, j;for(i=0; i<MAXN; i++)isprime[i] = true;for(i=2; i<=500; i++){for(j=i*i; j<=MAXN; j+=i)isprime[j] = false;}int idx = 1;for(i=2; i<=MAXN; i++){if(isprime[i])prime[idx++] = i;}prime[1] = 3;prime[2] = 4;fib[0] = fib[1] = 1;bool flag = false;for(i=2; i<=MAXN; i++){if(flag){fib[i] = fib[i-1] + fib[i-2]/10;flag = 0;}else {fib[i] = fib[i-1] + fib[i-2];}if(fib[i]>1e9){fib[i]/=10;flag = true;}}int n;while(scanf("%d", &n)!=EOF)printf("%d\n", (int)fib[prime[n]-1]);
}