1 files changed, 75 insertions, 0 deletions
diff --git a/day14.cc b/day14.cc
new file mode 100644
index 0000000..55b02fd
--- /dev/null
+++ b/day14.cc
@@ -0,0 +1,75 @@
+#include <array>
+#include <bitset>
+#include <functional>
+#include <iostream>
+#include <numeric>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+template <typename T>
+auto knothash(T iter, int n=64)
+{
+	vector<uint8_t> v(256);
+	iota(begin(v), end(v), 0);
+
+	uint8_t skip = 0, pos = 0, delta;
+
+	for (int j = 0; j < n; j++)
+		for (auto i : iter) {
+			reverse(begin(v), begin(v) + i);
+			delta = i + skip++;
+			rotate(begin(v), begin(v) + delta, end(v));
+			pos += delta;
+		}
+	rotate(begin(v), end(v) - pos, end(v));
+
+	return move(v);
+}
+
+int
+main() {
+	string line;
+	cin >> line;
+
+	int p1{0};
+	int p2{0};
+
+	array<array<int, 128>, 128> a;
+
+	for (int i = 0; i < 128; ++i) {
+		string s = line + "-" + to_string(i);
+		s.append({17,31,73,47,23});
+
+		vector<uint8_t> v{knothash(s)};
+
+		int j = 0;
+		for (auto r = begin(v); r != end(v); advance(r, 16)) {
+			bitset<8> b =
+			    accumulate(r, r + 16, 0, bit_xor<uint8_t>());
+			p1 += b.count();
+			for (int n = 7; n >= 0; n--)
+				a[i][j++] = -b[n];
+		}
+	}
+
+	std::function<void (int,int,int)> fill = [&](int i, int j, int c) {
+		if (i < 0 || i >= size(a) ||
+		    j < 0 || j >= size(a) ||
+		    a[i][j] >= 0)
+			return;
+		a[i][j] = c;
+		fill(i-1,  j,  c);
+		fill(i+1,  j,  c);
+		fill( i,  j-1, c);
+		fill( i,  j+1, c);
+	};
+
+	for (int i = 0; i < size(a); i++)
+		for (int j = 0; j < size(a[i]); j++)
+			if (a[i][j] < 0)
+				fill(i, j, ++p2);
+
+	cout << p1 << endl << p2 << endl;	// 8226 1128
+}