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找到一亿内所有素数并写入文件用时 35秒.

#include "math.h"

#include "stdio.h" #include "stdlib.h" #include "time.h"

int isP(int num,int *p) { int i; int len=p[0]; int flag=1; p++;

for(i=0;i

return flag; }

int fun(int num) { int cnt=(int)sqrt((double)num);

if(cnt) while(num%cnt) cnt--; return cnt==1; }

void main() { int h=100000000; int l=2; int len=sqrt((double)h)+1; int n=len/log(len)+1; long i; clock_t start,end; int *a=(int)calloc(sizeof(int),(int) (2*len/log(len))); FILE *fp=fopen("p.txt","w");

a[0]=1; a[1]=2;

for(i=3;i

printf("num:%d,n:%d,len:%d\n",a[0], (int)(3*len/(log(len)*2)),len);

start=clock();

if(2<=l) fprintf(fp,"%d\n",2); for(i=l+!(l%2);i<=h;i+=2) if(isP(i,a)) fprintf(fp,"%d\n",i);

end=clock();

fclose(fp);

printf("%f\n",(double)(end-start)/CLOCKS_PER_SEC);

free(a); }

}