UVa/10235 - Simply Emirp/10235.cpp

   1 #include <stdlib.h>
   2 #include <iostream>
   3 #include <math.h>
   4
   5 using namespace std;
   6
   7 bool esPrimo(const int &n){
   8      if (n % 2 == 0)
   9         return false;
  10      else{
  11         int raiz = (int)ceil(sqrt(n)) + 1;
  12         for (int i=3; i<raiz; i += 2)
  13             if (n % i == 0)
  14                   return false;
  15         return true;
  16      }
  17 }
  18
  19 int voltear(int n){
  20     int r=0;
  21     while (n > 0){
  22           r = r * 10 + n % 10;
  23           n /= 10;
  24     }
  25     return r;
  26 }
  27
  28 int main()
  29 {
  30     int n;
  31     while (cin >> n){
  32           if (!esPrimo(n))
  33              cout << n << " is not prime.\n";
  34           else{
  35                 int inverso = voltear(n);
  36                 if (inverso != n && esPrimo(inverso))
  37                    cout << n << " is emirp.\n";
  38
  39                 else
  40                    cout << n << " is prime.\n";
  41           }
  42     }
  43     return 0;
  44 }