Day 8 of 2018 advent of code. Loads input from file instead of stdin so that's very slow, and I put almost no effort into making it faster after it was done.

2018day8.cpp

#include <chrono>
#include <cstdio>
#include <fstream>
#include <string>
#include <vector>

#include "tree.h" // for TreeNode

using namespace std::chrono;

TreeNode* root = nullptr;

std::vector<short> input;

int totalmetadata;

void prnt(TreeNode* n) {
	static char lbl = 'A';
	std::printf("%c:\n children: %d\n metadatasum: %d\n\n", lbl++, n->childcount, n->metadatasum);
	for (int i = 0; i < n->children.size(); i++) {
		prnt(n->children[i]);
	}
}

int parse(int begin = 0, TreeNode* parent = nullptr) {
	// starting at 0 should be the beginning of a new node
	TreeNode* ptr = nullptr;
	if (parent == nullptr) {
		root = new TreeNode(nullptr, input[begin]);
		ptr = root;
	}
	else {
		parent->children.push_back(new TreeNode(parent, input[begin]));
		ptr = parent->children.back();
	}

	int totalparsed = 2; // parsing at least two things for each node
	for (int i = 0; i < input[begin]; i++) {
		totalparsed += parse(begin + totalparsed, ptr);
	}

	for (int i = 0; i < input[begin + 1]; i++) {
		ptr->metadatasum += input[begin + totalparsed + i];
		ptr->metadata.push_back(input[begin + totalparsed + i]);
	}

	totalmetadata += ptr->metadatasum;
	
	return totalparsed + input[begin + 1]; // add number of metadata items to this
}

int val(TreeNode* n) {
	int sum = 0;

	if (n->childcount) {
		for (int i : n->metadata) {
			if (i <= n->childcount) {
				sum += val(n->children[i - 1]);
			}
		}
	}
	else {
		for (int i : n->metadata) {
			sum += i;
		}
	}

	return sum;
}

int main() {
	{ // load input
		std::puts("Loading file...");
		std::ifstream infile("bqgnir");
		short nval;
		while (infile >> nval) input.push_back(nval);
	}

	// did this to compete with people who use stdin for the input unlike me
	std::puts("File loaded, starting parsing and puzzle solving.");

	steady_clock::time_point t1 = steady_clock::now();

	parse();
	int rootval = val(root);

	steady_clock::time_point t2 = steady_clock::now();
	duration<double> time_span = duration_cast<duration<double>>(t2 - t1);
	std::printf("Took %.2f seconds to parse nodes into tree and perform calculations.\n", time_span.count());

	std::printf("Part 1: %d\n", totalmetadata);
	std::printf("Part 2: %d\n", rootval);

	delete root;

	return 0;
}

tree.h

#ifndef TREE_H
#define TREE_H

#include <vector>

class TreeNode {
public:
	TreeNode* parent; // nullptr if root
	std::vector<TreeNode*> children;
	int childcount;
	int metadatasum;
	std::vector<int> metadata;

	TreeNode(TreeNode* _parent, int _childcount):
		parent(_parent),
		childcount(_childcount),
		metadatasum(0)
	{};

	TreeNode(int _childcount):
		parent(nullptr),
		childcount(_childcount),
		metadatasum(0)
	{};

	~TreeNode() {
		if (childcount) {
			for (int i = 0; i < childcount; i++) {
				delete children[i];
			}
		}
	};
};

#endif