"Bzoj" 2818:GCD (Euler function/Möbius)

http://www.lydsy.com/JudgeOnline/problem.php?id=2818

I am very SB lost the original to do a question up.

In fact, the problem can be more simple.

Set

$ $f [i]=1+2 \times \phi (i) $$

So the answer is

$$\sum_{p is prime number} f[n/p]$$

I lost the original question ... Don't write it.

#include <cstdio> #include <cstring> #include <cmath> #include <string> #include <iostream > #include <algorithm> #include <queue> #include <set> #include <map>using namespace std; typedef long Long LL; #define REP (i, n) for (int i=0; i< (n); ++i) #define FOR1 (i,a,n) for (int i= (a); i<= (n); ++i) #define For2 (i,a,n) for (int i= (a);i< (n), ++i) #define FOR3 (i,a,n) for (int i= (a); i>= (n); i.) #define FOR4 (i,a,n) for (int i= ( a);i> (n); i) #define CC (i,a) memset (i,a,sizeof (i)) #define READ (a) a=getint () #define PRINT (a) printf ("%d", a) # Define DBG (x) cout << (#x) << "=" << (x) << endl#define error (x) (! x)? puts ("Error"): 0) Inline const int Getint () {int r=0, k=1; char C=getchar (); for (; c< ' 0 ' | | C> ' 9 '; C=getchar ()) if (c== '-') k=-1; for (; c>= ' 0 ' &&c<= ' 9 '; C=getchar ()) r=r*10+c-' 0 '; return k*r; } #define RDM (x, i) for (int i=ihead[x]; i; i=e[i].next) const int N=10000005;int p[n], CNT, np[n], mu[n], g[n], Sum[n];voID init () {Mu[1]=1;for2 (I, 2, N) {if (!np[i]) p[++cnt]=i, Mu[i]=-1, G[i]=1;for1 (J, 1, CNT) {int t=p[j]*i; if (t>=n) break ; Np[t]=1;if (i%p[j]==0) {mu[t]=0; g[t]=mu[i]; break;} Mu[t]=-mu[i]; G[t]=mu[i]-g[i];}} For2 (i, 1, N) sum[i]=sum[i-1]+g[i];} int main () {init (); int n=getint (); ll ans=0;int pos;for (int i=1; i<=n; i=pos+1) {pos=min (n/(n/i), n/(n/i)); ans+= (LL) ( SUM[POS]-SUM[I-1]) * (n/i) * (n/i);} printf ("%lld\n", ans); return 0;}

　　

Description

Given an integer n, 1<=x,y<=n and gcd (x, y) are prime
Number pairs (x, y) how many pairs.

Input

An integer n

Output

Title

Sample Input4

Sample Output4hint

Hint

For examples (2,2), (2,4), (3,3), (4,2)

1<=n<=10^7

Source

Hubei Province Team Mutual test

"Bzoj" 2818:GCD (Euler function/Möbius)