static IntAndLong GetNumWithoutPreambleProperty(int preambleLength, long[] input, List <long> preamble)
{
IntAndLong numWithoutPreambleProperty = new IntAndLong();
for (int i = preambleLength; i < input.Length; i++)
{
for (int j = preamble.Count - 1; j > 0; j--)
{
long remainder = input[i] - preamble[j];
int index = preamble.IndexOf(remainder);
if (index == j)
{
break;
}
else if (preamble.IndexOf(remainder) != -1)
{
preamble.Add(input[i]);
preamble.RemoveAt(0);
break;
}
}
if (preamble.IndexOf(input[i]) == -1)
{
numWithoutPreambleProperty.IndexOfNum = i;
numWithoutPreambleProperty.Num = input[i];
break;
}
}
return(numWithoutPreambleProperty);
}
static long GetEncryptionWeakness(long[] input, IntAndLong numWithoutPreambleProperty)
{
List <long> inputUntilNum = new List <long>();
long encryptionWeakness = 0;
for (int i = 0; i < numWithoutPreambleProperty.IndexOfNum - 1; i++)
{
inputUntilNum.Add(input[i]);
long sum = input[i];
for (int j = i + 1; j < numWithoutPreambleProperty.IndexOfNum; j++)
{
inputUntilNum.Add(input[j]);
sum += input[j];
if (sum == numWithoutPreambleProperty.Num)
{
inputUntilNum.Sort();
encryptionWeakness = inputUntilNum[0] + inputUntilNum[inputUntilNum.Count - 1];
break;
}
else if (sum > numWithoutPreambleProperty.Num)
{
break;
}
}
inputUntilNum.Clear();
}
return(encryptionWeakness);
}
static void Main()
{
long[] input = File.ReadAllLines("input.txt").Select(long.Parse).ToArray();
List <long> preamble = new List <long>();
const int preambleLength = 25;
for (int i = 0; i < preambleLength; i++)
{
preamble.Add(input[i]);
}
IntAndLong numWithoutPreambleProperty = GetNumWithoutPreambleProperty(preambleLength, input, preamble);
Console.WriteLine("The encryption weakness is {0}.", GetEncryptionWeakness(input, numWithoutPreambleProperty));
}