HDU 2136 Largest prime factor

 

http://acm.hdu.edu.cn/showproblem.php?pid=2136

 

解题思路：用筛选法，求出输入的N值最大的素数的编号

 

#include<stdio.h>#define size 1000001int prime[size];int main(){int locate=0;int n,i,j;for(j=2;j<size;j++)prime[j]=-1;prime[1] = 0;/*筛选位置*/for(i=2; i<size; i++){if(prime[i]==-1){locate++;for(j=i;j<size;j+=i) prime[j]=locate;}} while(scanf("%d",&n)!=EOF)printf("%d/n",prime[n]);return 0;}