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+> bs;
 vi primes;

 void sieve(ll upper)
 {
     bs.set();
     bs.set(, false);
     bs.set(, false);
     for (ll i = ; 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 = , pf = primes[idx];
     while (n !=  && (pf*pf <= n))
     {
         while (n % pf == )
         {
             n /= pf;
             factors.push_back(pf);
         }
         pf = primes[++idx];
     }
     if (n != )  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 ;
 }