- Coprimes
For given integer N (1<=N<=104) find amount of positive numbers not greater than N that coprime with N. Let us call two positive integers (say, A and B, for example) coprime if (and only if) their greatest common divisor is 1. (i.e. A and B are coprime iff gcd(A,B) = 1).
Input
Input file contains integer N.
Output
Write answer in output file.
Sample Input
9
Sample Output
6
题目类型：Euler函数计算
算法分析：直接使用试除法求解即可
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#include <set> #include <bitset> #include <list> #include <map> #include <stack> #include <queue> #include <deque> #include <string> #include <vector> #include <ios> #include <iostream> #include <fstream> #include <sstream> #include <iomanip> #include <algorithm> #include <utility> #include <complex> #include <numeric> #include <functional> #include <cmath> #include <ctime> #include <climits> #include <cstdarg> #include <cstdio> #include <cstdlib> #include <cstring> #include <cctype> #include <cassert> using namespace std; const int INF = 0x7FFFFFFF; const int MOD = 1e9 + 7; const double EPS = 1e-10; const double PI = 2 * acos (0.0); const int maxn = 100000 + 66; long long GetEuler (long long val) { long long ans = val; for (long long i = 2; i * i <= val; i++) { if (val % i == 0) { ans -= ans / i; while (val % i == 0) { val /= i; } } } if (val > 1) ans -= ans / val; return ans; } int main() { // ifstream cin ("aaa.txt"); // freopen ("aaa.txt", "r", stdin); long long n; cin >> n; cout << GetEuler(n) << endl; return 0; } |