#coding exercise
Write a program to find the nth ugly number. An ugly number is one that has prime factors of only two, three or five
Solution an ugly number must be formed by multiplying 2,3 or 5 from a smaller number.

List<int> getUgly(int n)
{
var ret = new List<int>() {1};
// indexes for last candidates for corresponding multiples
int I2 = 0;
int I3 = 0;
int I5 = 0;
for (int i  = 0; i < ret.Count() && ret.Last() < n;i++)
{
 
   int min = min(GetProduct(ref ret, 2, I2 ),
                           GetProduct(ref ret, 3, I3),
                            GetProduct(ref ret, 5, I5));
   if (min == GetProduct(ref ret, 2, I2))
      I2  = I2 + 1;
   if (min == GetProduct(ref ret, 3, I3))
      I3  = I3 + 1;
   if (min == GetProduct(ref ret, 5, I5))
      I5  = I5 + 1;
   if (ret.Contains(min) == false) // this check can be commented out
        ret.Add(min);
}
return ret;
}
int GetProduct(ref ret, int multiplier, int index)
{
    return ret[index] * multiplier;
}
For example:
ret 1,2, 3, 4, 5, 6 ,8,9, 10, 12, 15
I2  6
I3  5
I5  3