poj1491
简单题
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
#include <iostream> #include <cstdlib> #include <cstdio> #include <cstring> #include <cmath> using namespace std; #define maxn 55 int n; int f[maxn]; int gcd(int a, int b) { if (b > 0) return gcd(b, a % b); return a; } void input() { for (int i = 0; i < n; i++) scanf("%d", &f[i]); } void work() { int numerator = 0; for (int i = 0; i < n; i++) for (int j = i + 1; j < n; j++) if (gcd(f[i], f[j]) == 1) numerator++; if (numerator == 0) { printf("No estimate for this data set.\n"); return; } printf("%.6f\n", sqrt(n * (n - 1) * 3.0 / numerator)); } int main() { // freopen("t.txt", "r", stdin); while (scanf("%d", &n), n) { input(); work(); } return 0; }