C

素数を列挙する関数

   ArrayList getPrimeNumber(long upper)
   {
       ArrayList arr = new ArrayList();
       bool[] flags = new bool[upper+1];
       arr.Add(2);
       for (int i = 2; i < upper + 1; i += 2) flags[i] = true;
       for (int i = 3; i < upper + 1; i += 2)
       {
           if (!flags[i])
           {
               arr.Add(i);
               for (int j = i; j < upper+1; j+=i)flags[j] = true;
           }
       }
       return arr;
   }