uva 10280(欧拉函数)
题意:找n以内有多少对互质的数。
思路:欧拉函数预处理一下,然后答案等于(∑Euler(i)-1)*2 + 1 i从1到n。
代码如下:
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 /************************************************** 2 * Author : xiaohao Z 3 * Blog : http://www.cnblogs.com/shu-xiaohao/ 4 * Last modified : 2014-03-28 18:19 5 * Filename : uva_10820.cpp 6 * Description : 7 * ************************************************/ 8 9 #include <iostream> 10 #include <cstdio> 11 #include <cstring> 12 #include <cstdlib> 13 #include <cmath> 14 #include <algorithm> 15 #include <queue> 16 #include <stack> 17 #include <vector> 18 #include <set> 19 #include <map> 20 #define MP(a, b) make_pair(a, b) 21 #define PB(a) push_back(a) 22 23 using namespace std; 24 typedef long long ll; 25 typedef pair<int, int> pii; 26 typedef pair<unsigned int,unsigned int> puu; 27 typedef pair<int, double> pid; 28 typedef pair<ll, int> pli; 29 typedef pair<int, ll> pil; 30 31 const int INF = 0x3f3f3f3f; 32 const double eps = 1E-6; 33 const int LEN = 500010; 34 int dp[LEN]; 35 36 int Euler(int n) 37 { 38 int ans = n; 39 for(int i=2; i<=sqrt(n); i++){ 40 if(n%i == 0){ 41 ans = ans / i * (i-1); 42 while(n%i == 0) n /= i; 43 } 44 } 45 if(n > 1) ans = ans / n * (n-1); 46 return ans; 47 } 48 49 int main() 50 { 51 // freopen("in.txt", "r", stdin); 52 53 int n; 54 dp[0] = 0; 55 for(int i=1; i<LEN; i++) 56 dp[i] = dp[i-1] + Euler(i); 57 while(cin >> n){ 58 if(!n) break; 59 cout << (dp[n]-1) * 2 + 1 << endl; 60 } 61 return 0; 62 }
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