线性筛法

#include<bits/stdc++.h>#define ll long longusing namespace std;const int N = 1e5+100;bool vis[N]void init(){    vis[1] = true;    for(int i = 2;i < N;i ++){        if(vis[i] == false)        v.push_back(i);        for(int j = 0;j < v.size()&&i*v[j] < N;j ++){            vis[i*v[j]] = true;            if(i%v[j] == 0) break;        }    }}