# C#: Project Euler Solution to Problem 35

Project Euler Problem #35

The number, 197, is called a circular prime because all rotations of the digits: 197, 971, and 719, are themselves prime.

There are thirteen such primes below 100: 2, 3, 5, 7, 11, 13, 17, 31, 37, 71, 73, 79, and 97.

How many circular primes are there below one million?

```static void Main(string[] args) { DateTime d1 = DateTime.Now; LinkedList<int> unique_CirclePrime = new LinkedList<int>(); LinkedList<int> tempList = new LinkedList<int>(); int currentPrime = 1; while (currentPrime <= 1000000) { string initNum2Rotate = currentPrime.ToString(); int c = 0; int placeHolder = 0; for (int j = 0; j < initNum2Rotate.Length; j++) { int previousdisplay = 0; string displayString = ""; for (int i = 0; i < initNum2Rotate.Length; i++) { if (placeHolder == initNum2Rotate.Length) placeHolder = 0; int display = (placeHolder + c); if (display == initNum2Rotate.Length) display = 0;   if (display > initNum2Rotate.Length) display = previousdisplay + 1;placeHolder++; string gluestring = initNum2Rotate[display].ToString(); previousdisplay = display; displayString += gluestring; } c++; tempList.AddLast( int.Parse(displayString) ); } bool allprimes = false; foreach (int item in tempList) { if (isPrime(item)) allprimes = true; else { allprimes = false; break; } } if (allprimes) { foreach (int item in tempList) { if (!unique_CirclePrime.Contains(item)) unique_CirclePrime.AddLast(item); } } tempList.Clear(); currentPrime++; }   int counter = 1; foreach (var item in unique_CirclePrime) { Console.WriteLine(item + " " + isPrime(item) + " " + counter); counter++; } DateTime d2 = DateTime.Now;   Console.WriteLine("Total Length of Unique Circular Primes : "+ unique_CirclePrime.Count); Console.WriteLine("time : " + (d2 - d1)); }   public static bool isPrime(int n) { if (n == 1) return false; if (n == 2) return true; for (int i = 2; i < n; ++i) { if ((n % i) == 0) return false; } return true; }```