//http://en.wikipedia.org/wiki/Truncatable_prime
public override long Solve()
{
long sum = 0;
var primes = Primes.CalculatePrimesBelow(1000000);
foreach(var prime in primes) {
bool truncatable = true;
if (PossibleTruncatablePrime(prime)) {
var leftToRightTruncate = new Truncate(prime, TruncateMethod.LeftToRight);
while (leftToRightTruncate.CanTruncate()) {
if (!primes.Contains(leftToRightTruncate.NextValue())) {
truncatable = false;
break;
}
}
var rightToLeftTruncate = new Truncate(prime, TruncateMethod.RightToLeft);
while (rightToLeftTruncate.CanTruncate()) {
if (!primes.Contains(rightToLeftTruncate.NextValue())) {
truncatable = false;
break;
}
}
if (truncatable) sum += prime;
}
}
return sum;
}
public void Truncate_Right_To_Left()
{
var truncate = new Truncate(345, TruncateMethod.RightToLeft);
Assert.IsTrue(truncate.CanTruncate());
Assert.AreEqual(34, truncate.NextValue());
Assert.IsTrue(truncate.CanTruncate());
Assert.AreEqual(3, truncate.NextValue());
Assert.IsFalse(truncate.CanTruncate());
Assert.AreEqual(3, truncate.CurrentValue());
}
public void Truncate_Left_To_Right()
{
var truncate = new Truncate(234, TruncateMethod.LeftToRight);
Assert.IsTrue(truncate.CanTruncate());
Assert.AreEqual(34, truncate.NextValue());
Assert.IsTrue(truncate.CanTruncate());
Assert.AreEqual(4, truncate.NextValue());
Assert.IsFalse(truncate.CanTruncate());
Assert.AreEqual(4, truncate.CurrentValue());
}
//http://en.wikipedia.org/wiki/Truncatable_prime
public override long Solve()
{
long sum = 0;
var primes = Primes.CalculatePrimesBelow(1000000);
foreach (var prime in primes)
{
bool truncatable = true;
if (PossibleTruncatablePrime(prime))
{
var leftToRightTruncate = new Truncate(prime, TruncateMethod.LeftToRight);
while (leftToRightTruncate.CanTruncate())
{
if (!primes.Contains(leftToRightTruncate.NextValue()))
{
truncatable = false;
break;
}
}
var rightToLeftTruncate = new Truncate(prime, TruncateMethod.RightToLeft);
while (rightToLeftTruncate.CanTruncate())
{
if (!primes.Contains(rightToLeftTruncate.NextValue()))
{
truncatable = false;
break;
}
}
if (truncatable)
{
sum += prime;
}
}
}
return(sum);
}