[反演 莫队算法] HDU 4676 Sum Of Gcd

#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<cmath>
#include<vector>
#include<cstring>
#define cl(x) memset(x,0,sizeof(x))
using namespace std;
typedef long long ll;

inline char nc(){
static char buf[100000],*p1=buf,*p2=buf;
if (p1==p2) { p2=(p1=buf)+fread(buf,1,100000,stdin); if (p1==p2) return EOF; }
return *p1++;
}

inline void read(int &x){
char c=nc(),b=1;
for (;!(c>='0' && c<='9');c=nc()) if (c=='-') b=-1;
for (x=0;c>='0' && c<='9';x=x*10+c-'0',c=nc()); x*=b;
}

const int N=20005;

int phi
;
vector<int> fac
;
inline void Pre(int n=20000){
phi[1]=1;
int i,j;
for (int i=1;i<=n;i++)
if(!phi[i])
for (j=i;j<n;j+=i){
if (!phi[j]) phi[j]=j;
phi[j]-=phi[j]/i;
}
for (int i=1;i<=n;i++)
for (int j=i;j<=n;j+=i)
fac[j].push_back(i);
}

int n,a
;
int pos
;
struct event{
int l,r,idx;
bool operator < (const event &B)const{ return pos[l]==pos[B.l]?r<B.r:pos[l]<pos[B.l]; }
}eve
;
int tot;ll ans
;

int num
;
ll cur;

inline void add(int t){
for (int i=0;i<(int)fac[t].size();i++){
int x=fac[t][i];
cur+=(ll)num[x]*phi[x]; num[x]++;
}
}
inline void del(int t){
for (int i=0;i<(int)fac[t].size();i++){
int x=fac[t][i];
num[x]--; cur-=(ll)num[x]*phi[x];
}
}

int main(){
int T,Case=0;
freopen("t.in","r",stdin);
freopen("t.out","w",stdout);
read(T); Pre();
while (T--){
printf("Case #%d:\n",++Case);
read(n); for (int i=1;i<=n;i++) read(a[i]);
read(tot); for (int i=1;i<=tot;i++) read(eve[i].l),read(eve[i].r),eve[i].idx=i;
int B=sqrt((double)n)+1;
for (int i=1;i<=n;i++) pos[i]=(i-1)/B+1;
sort(eve+1,eve+tot+1);

int l=1,r=0;
for (int i=1;i<=tot;i++){
while (r<eve[i].r) add(a[++r]);
while (r>eve[i].r) del(a[r--]);
while (l<eve[i].l) del(a[l++]);
while (l>eve[i].l) add(a[--l]);
ans[eve[i].idx]=cur;
}

for (int i=1;i<=tot;i++)
printf("%I64d\n",ans[i]);
cl(num); cur=0;
}
return 0;
}