1 files changed, 87 insertions, 0 deletions
diff --git a/2021/day14/day14.cpp b/2021/day14/day14.cpp
new file mode 100644
index 0000000..63656b6
--- /dev/null
+++ b/2021/day14/day14.cpp
@@ -0,0 +1,87 @@
+#include <iostream>
+#include <fstream>
+#include <vector>
+#include <string>
+#include <map>
+#include "../utils.h"
+
+std::map<std::string, long> apply (std::map<std::string, long> pairs, 
+	std::map<std::string, char> rules, std::map<char, long> &count) 
+{
+	std::map<std::string, long> next = pairs;
+	for (auto &pair : pairs) {
+		char c = rules[pair.first];
+		count[c] += pair.second;
+		std::string l; 
+		l.push_back(pair.first[0]);
+		l.push_back(c);
+		std::string r; 
+		r.push_back(c);
+		r.push_back(pair.first[1]);
+		next[pair.first] -= pair.second;
+		next[l] += pair.second;
+		next[r] += pair.second;
+	}
+	return next;
+}
+
+void to_pairs (std::string init, std::map<std::string, long> &pairs) {
+	for (std::size_t i=0; i<init.size()-1; i++) {
+		std::string seg = init.substr(i, 2);
+		pairs[seg] ++;
+	}
+}
+
+long tally (std::map<char, long> map) {
+	std::vector<long> f;
+	for (auto p : map) {
+	       	f.push_back(p.second);
+		std::cout << p.first << " " << p.second << std::endl;	
+	}
+	std::sort(f.begin(), f.end());
+	return f[f.size()-1] - f[0];
+}
+
+int main (int argc, char *argv[]) {
+	std::string raw;
+	std::getline(std::ifstream(argv[1]), raw, '\0');
+	std::vector<std::string> parts, strrules;
+	split(parts, raw, "\n\n");
+	split(strrules, parts[1], "\n");
+
+	std::string polymer = parts[0];
+	std::cout << "starting polymer: " << polymer << std::endl;
+
+	std::map<std::string, long> pairs;
+	std::map<std::string, char> rules;
+	for (auto strrule : strrules) {
+		if (strrule.size() == 0) continue;
+		std::vector<std::string> rl;
+		split(rl, strrule, " -> ");
+		rules[rl[0]] = rl[1][0];
+		pairs[rl[0]] = 0;
+	}
+
+	to_pairs(polymer, pairs);
+	
+	std::map<char, long> count;
+	for (auto pair : pairs) {
+		count[pair.first[0]] = 0;
+		count[pair.first[1]] = 0;
+	}
+
+	for (char c : polymer) {
+		count[c] ++;
+	}
+
+	long iter = 10;
+	if (argc > 2) iter = atoi(argv[2]);
+	for (long i=0; i<iter; i++) {
+		pairs = apply(pairs, rules, count);
+	}
+
+	long res = tally(count);
+	std::cout << "most common - least common: " << res << std::endl;
+
+	return 0;
+}