poj 3048 Max Factor

#include <stdio.h>#include <math.h>#include <string.h>const int maxn=20000+5;bool vis[maxn];int Prime[maxn],cnt;void init(){int i,k;cnt=0;memset(vis,true,sizeof vis);vis[0]=vis[1]=false;for(i=2;i<=maxn;i++){if(!vis[i]) continue;Prime[cnt++]=i;for(k=i+i;k<=maxn;k+=i){vis[k]=false;}}}int Maxfactor(int x){int i,j,u,max=-1;for(i=2,j=0;x!=1;i++,j++){u=Prime[j];while(!(x%u)){x/=u;if(max<u) max=u;}}return max;}