素数筛——Eratosthenes 素数筛、Euler 素数筛

/*****************************************************
> File Name: liner_filter.cpp
> Author: Yuji CAO
> Mail: 1007171627@qq.com
> Created Time: 二  6/13 12:11:11 2017
****************************************************/

#include<map>
#include<vector>
#include<unordered_set>
#include<unordered_map>
#include<list>
#include<queue>
#include<deque>
#include<stack>
#include<iostream>
#include<set>
using namespace std;
/**
* Eratosthenes 素数筛
**/
int prime_nlogn(int n) {
vector<int> prime;
unordered_set<int> checkout;
for (int i = 2; i <= n; ++i) {
if (!checkout.count(i)) prime.push_back(i);
for (int j = i * 2; j <= n; j += i) {
checkout.insert(j);
}
}
return prime.size();
}
/**
* Euler 素数筛
**/
int prime_n(int n) {
vector<int> prime;
unordered_set<int> checkout;
for (int i = 2; i <= n; ++i) {
if (!checkout.count(i)) prime.push_back(i);
for (int j = 0; j < prime.size(); ++j) {
if (prime[j] * i > n) break;
checkout.insert(prime[j] * i);
if (i % prime[j] == 0) break;
}
}
return (int) prime.size();
}

int main() {
while (true) {
int n;
cin>>n;
int a = prime_n(n);
int b = prime_nlogn(n);
cout<<a<<":"<<b<<endl;
}
return 0;
}