UVa 10179 - Irreducable Basic Fractions

欧拉函数

/*************************************************************************
    > File Name: 10179.cpp
    > Author: Toy
    > Mail: ycsgldy@163.com 
    > Created Time: 2013年06月04日 星期二 20时19分18秒
 ************************************************************************/

#include <algorithm>
#include <iostream>
#include <iomanip>
#include <cstring>
#include <cstdlib>
#include <climits>
#include <sstream>
#include <fstream>
#include <cstdio>
#include <string>
#include <vector>
#include <queue>
#include <cmath>
#include <stack>
#include <map>
#include <set>

using namespace std;
const int INF = 0x7fffffff;
typedef pair<int,int> II;
typedef vector<int> IV;
typedef vector<II> IIV;
typedef vector<bool> BV;
typedef long long i64;
typedef unsigned long long u64;
typedef unsigned int u32;
#define For(t,v,c) for(t::const_iterator v=c.begin(); v!=c.end(); ++v)
#define IsComp(n) (_c[n>>6]&(1<<((n>>1)&31)))
#define SetComp(n) _c[n>>6]|=(1<<((n>>1)&31))
const int MAXP = 46341; //sqrt(2^31)
const int SQRP = 216; //sqrt(MAX)
int _c[(MAXP>>6)+1];
IV primes;

void prime_sieve ( ) {
	for ( int i = 3; i <= SQRP; i += 2 ) 
		if ( !IsComp ( i ) ) for ( int j = i * i; j <= MAXP; j += i + i ) SetComp ( j );
	primes.push_back ( 2 );
	for ( int i = 3; i <= MAXP; i += 2 ) 
		if ( !IsComp ( i ) ) primes.push_back ( i );
}

int euler_phi ( int n ) {
	int ans = n;
	int sn = sqrt ( n );
	For ( IV, it, primes ) {
		int prime = *it;
		if ( prime > sn ) break;
		if ( n % prime ) continue;
		for ( ; n % prime == 0; n /= prime ) ;
		ans /= prime;
		ans *= ( prime - 1 );
		sn = sqrt ( n );
	}
	if ( n > 1 ) ans /= n, ans *= ( n - 1 );
	return ans;
}

int Case;
int main ( ) {
	prime_sieve();
	while ( scanf ( "%d", &Case ) == 1 ) {
		if ( !Case ) break;
		printf ( "%d\n", euler_phi ( Case ) );
	}
    return 0;
}