【欧拉函数】 HDOJ 2824 The Euler function

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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();}// headLL 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;}

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