UVa 10179 - Irreducable Basic Fractions

　　题目大意：给一个正整数n，求出在[1, n]区间内和n互质的正整数的个数。Euler's Totient（欧拉函数）的直接应用。

#include <cstdio>
#include <vector>
#include <algorithm>
#include <bitset>
using namespace std;
typedef vector<int> vi;
typedef long long ll;
#define MAXN 10000000

bitset<MAXN+100> bs;
vi primes;

void sieve(ll upper)
{
    bs.set();
    bs.set(0, false);
    bs.set(1, false);
    for (ll i = 2; i <= upper; i++)
    {
        if (bs.test((size_t)i))
            for (ll j = i*i; j <= upper; j++)
                bs.set((size_t)j, false);
        primes.push_back((int)i);
    }
}

vi primeFactors(ll n)
{
    vi factors;
    int idx = 0, pf = primes[idx];
    while (n != 1 && (pf*pf <= n))
    {
        while (n % pf == 0)
        {
            n /= pf;
            factors.push_back(pf);
        }
        pf = primes[++idx];
    }
    if (n != 1)  factors.push_back(n);
    return factors;
}

int main()
{
#ifdef LOCAL
    freopen("in", "r", stdin);
#endif
    sieve(MAXN);
    int n;
    while (scanf("%d", &n) && n)
    {
        vi factors = primeFactors(n);
        vi::iterator last = unique(factors.begin(), factors.end());
        int result = n;
        for (vi::iterator it = factors.begin(); it != last; it++)
            result = result - result/(*it);
        printf("%d\n", result);
    }
    return 0;
}