BZOJ1968: [Ahoi2005]COMMON 约数研究 线性筛

Code:

#include <cstdio> 
#include <algorithm>    
#define N 1000004 
#define setIO(s) freopen(s".in","r",stdin) 
using namespace std;  
int tot; 
int f[N],prime[N],vis[N],sum[N];
int main() 
{ 
    //setIO("input");  
    int n,i,j; 
    scanf("%d",&n);   
    sum[1]=f[1]=1; 
    for(i=2;i<=n;++i) 
    { 
        if(!vis[i]) prime[++tot]=i,f[i]=2;   
        for(j=1;j<=tot&&1ll*i*prime[j]<=1ll*n;++j)  
        {
            vis[i*prime[j]]=1;
            if(i%prime[j]==0) 
            { 
                int h=i; 
                for(;h%prime[j]==0;h/=prime[j]); 
                f[i*prime[j]]=f[h]+f[i]; 
                break;
            }
            else 
            {
                f[i*prime[j]]=f[i]*f[prime[j]];
            }
        }
        sum[i]=sum[i-1]+f[i];
    }
    printf("%d\n",sum[n]); 
    return 0; 
}

标签：约数,Ahoi2005,BZOJ1968,int,sum,setIO,include,define
来源： https://www.cnblogs.com/guangheli/p/11491101.html