【欧拉函数】 HDOJ 2824 The Euler function

筛选法求欧拉函数。。。

#include <iostream>  
#include <queue>  
#include <stack>  
#include <map>  
#include <set>  
#include <bitset>  
#include <cstdio>  
#include <algorithm>  
#include <cstring>  
#include <climits>  
#include <cstdlib>
#include <cmath>
#include <time.h>
#define maxn 3000005
#define maxm 3000005
#define eps 1e-10
#define mod 998244353
#define INF 999999999
#define lowbit(x) (x&(-x))
#define mp mark_pair
#define ls o<<1
#define rs o<<1 | 1
#define lson o<<1, L, mid  
#define rson o<<1 | 1, mid+1, R
#define debug(x) printf("AA x = %d BB\n", x);
//#pragma comment (linker,"/STACK:102400000,102400000")
typedef long long LL;
//typedef int LL;
using namespace std;
LL powmod(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base%mod;base=base*base%mod;b/=2;}return res;}
void scanf(int &__x){__x=0;char __ch=getchar();while(__ch==' '||__ch=='\n')__ch=getchar();while(__ch>='0'&&__ch<='9')__x=__x*10+__ch-'0',__ch = getchar();}
// head

LL phi[maxn];

void init(void)
{
	phi[1] = 1;
	for(int i = 2; i <= 3000000; i++)
		if(!phi[i])
			for(int j = i; j <= 3000000; j += i) {
				if(!phi[j]) phi[j] = j;
				phi[j] = phi[j] / i * (i-1);
			}
	for(int i = 1; i <= 3000000; i++) phi[i] += phi[i-1];
}
int main(void)
{
	init();
	int a, b;
	while(scanf("%d%d", &a, &b)!=EOF) {
		printf("%I64d\n", phi[b] - phi[a-1]);
	}
	return 0;
}