public static int First(string input)
{
// lookup table for number of set bits for each hex digit
Dictionary <char, int> hexBits = new Dictionary <char, int>
{
['0'] = 0,
['1'] = 1,
['2'] = 1,
['3'] = 2,
['4'] = 1,
['5'] = 2,
['6'] = 2,
['7'] = 3,
['8'] = 1,
['9'] = 2,
['a'] = 2,
['b'] = 3,
['c'] = 2,
['d'] = 3,
['e'] = 3,
['f'] = 4,
};
var used = 0;
// over all hashes...
for (int i = 0; i < 128; i++)
{
var hash = Day10.Second($"{input}-{i}");
// sum the number of set bits.
foreach (var c in hash)
{
used += hexBits[c];
}
}
return(used);
}
public static int Second(string input)
{
Dictionary <char, string> hexCharBinString = new Dictionary <char, string> {
['0'] = "0000",
['1'] = "0001",
['2'] = "0010",
['3'] = "0011",
['4'] = "0100",
['5'] = "0101",
['6'] = "0110",
['7'] = "0111",
['8'] = "1000",
['9'] = "1001",
['a'] = "1010",
['b'] = "1011",
['c'] = "1100",
['d'] = "1101",
['e'] = "1110",
['f'] = "1111",
};
bool[,] lines = new bool[128, 128];
for (int y = 0; y < 128; y++)
{
var hash = Day10.Second($"{input}-{y}");
var bits = string.Join("", hash.Select(c => hexCharBinString[c]));
for (int x = 0; x < 128; x++)
{
lines[x, y] = bits[x] == '1';
}
}
var graphInput = "";
for (int y = 0; y < 128; y++)
{
for (int x = 0; x < 128; x++)
{
if (lines[x, y])
{
var adjacents = new List <int>();
if (y > 0 && lines[x, y - 1])
{
adjacents.Add(x + (y - 1) * 128);
}
if (y < 127 && lines[x, y + 1])
{
adjacents.Add(x + (y + 1) * 128);
}
if (x > 0 && lines[x - 1, y])
{
adjacents.Add((x - 1) + y * 128);
}
if (x < 127 && lines[x + 1, y])
{
adjacents.Add((x + 1) + y * 128);
}
if (adjacents.Any())
{
graphInput += (x + y * 128) + " <-> " + string.Join(", ", adjacents) + '\n';
}
}
}
}
return(ConnectedGroups(graphInput, lines));
}
