欧拉函数求互质数的个数

互质数的个数（一）

思路：欧拉函数。
题目链接

import java.util.Scanner;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int t = sc.nextInt();
        while((t--)>0){
            long n = sc.nextLong();
            long ans = get_count(n);
            System.out.println(ans);
        }
    }
    public static long get_count(long n){
        if(n==1) return 1;
        long res = n;
        for(long i=2;i*i<=n;i++){
            if(n%i==0){
                res = res/i*(i-1);
                while(n%i==0) n/=i;
            }
        }
        if(n>1) res = res/n*(n-1);
        return res;
    }
}

欧拉筛筛选素数

package com.Test.Demo.oj;

import java.util.Scanner;

public class Main{
    static int n,count;
    static boolean[] flag = new boolean[100010];
    static int[] p = new int[100010],p_min = new int[100010];
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        n = sc.nextInt();
        get_p(n);
        for(int i=0;i<count;i++)System.out.println(p[i]);
    }
    public static void get_p(int n){ //欧拉筛 筛出2~n的素数
        for(int i=2;i<=n;i++){
            if(!flag[i]){
                p_min[i] = i;
                p[count++] = i;
            }
            for(int j=0;p[j]*i<=n;j++){
                flag[p[j]*i] = true;
                p_min[p[j]*i] = p[j];
                if(i%p[j]==0) break;
            }
        }
    }
}