Codeforces Round #563 (Div. 2)C. Ehab and a Special Coloring Problem

原文链接：传送门
思路：素数筛
代码：

#include"iostream"
#include"algorithm"
#include"cstring"
using namespace std;
long long  a[2000006],n;
int main(){
    cin>>n;
    long long  flag = 1;
    memset(a,0,sizeof(a));
    for(int i=2;i<=n;i++){
        if(a[i]==0){
            a[i]=flag;
            for(int j=i*2;j<=n;j+=i)
             if(a[j]==0)
              a[j]=flag;
              flag++;
        }
        cout<<a[i];
        if(i<n)
        cout<<" ";
    }
    return 0;
}