Part 1 of day 9 complete.

2022/9/Makefile

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+a.out: main.cpp
+	clang++ -std=c++2b -g -O0 main.cpp

2022/9/data_test.txt

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+R 4
+U 4
+L 3
+D 1
+R 4
+D 1
+L 5
+R 2

2022/9/main.cpp

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+#include <cmath>
+#include <fstream>
+#include <iostream>
+#include <set>
+#include <string>
+#include <unistd.h>
+#include <vector>
+
+void DebugPrint(std::pair<int, int> &head, std::pair<int, int> &tail,
+                std::set<std::pair<int, int> > &visited_positions)
+{
+	int x_min = head.first;
+	int y_min = head.second;
+	int x_max = head.first;
+	int y_max = head.second;
+
+	for(auto &pos : visited_positions)
+	{
+		x_min = std::min(x_min, pos.first);
+		x_max = std::max(x_max, pos.first);
+		y_min = std::min(y_min, pos.second);
+		y_max = std::max(y_max, pos.second);
+	}
+
+	for(auto i = 0; i < 50; ++i)
+		std::cout << std::endl;
+	std::cout << "X: " << x_min << " - " << x_max << std::endl;
+	std::cout << "Y: " << y_min << " - " << y_max << std::endl;
+	std::cout << std::endl;
+
+	for(auto y = y_min; y <= y_max; ++y)
+	{
+		for(auto x = x_min; x <= x_max; ++x)
+		{
+			if(head.first == x && head.second == y)
+				std::cout << "\033[1;30mH"; // head
+			else if(tail.first == x && tail.second == y)
+				std::cout << "\033[1;25mT"; // head
+			else if(visited_positions.contains({x, y}))
+				std::cout << "\033[1;31mX"; // red
+			else
+				std::cout << "\033[0m-"; // default white
+		}
+		std::cout << std::endl;
+	}
+	std::cout << "\033[0m"; // default white
+}
+
+int main()
+{
+	std::ifstream ifs("data.txt");
+	if(!ifs.is_open())
+	{
+		std::cerr << "Missing data.txt." << std::endl;
+		return -1;
+	}
+
+	unsigned long total = 0;
+	unsigned long total_pt2 = 0;
+
+	std::set<std::pair<int, int> > visited_positions;
+
+	std::pair<int, int> head = {0,0};
+	std::pair<int, int> tail = {0,0};
+
+	char dir;
+	int amt;
+
+	for(std::string line; std::getline(ifs, line); )
+	{
+		if(line == "")
+			continue;
+
+		dir = line[0];
+		amt = std::atoi(line.substr(2).c_str());
+
+		for(auto i = 0; i < amt; ++i)
+		{
+			// Move head:
+			switch(dir)
+			{
+			case 'U':
+				head.second--;
+				break;
+			case 'D':
+				head.second++;
+				break;
+			case 'L':
+				head.first--;
+				break;
+			case 'R':
+				head.first++;
+				break;
+			}
+
+			// Follow with tail:
+			const int x_diff = head.first - tail.first;
+			const int y_diff = head.second - tail.second;
+			if(std::abs(x_diff) > 1) // 2 away
+			{
+				tail.first += (head.first - tail.first) / 2;
+				if(y_diff)
+				{
+					int to_change = std::ceil(std::abs(head.second - tail.second) / 2.0);
+					if(y_diff < 0)
+						tail.second -= to_change;
+					else
+						tail.second += to_change;
+				}
+			}
+			if(std::abs(y_diff) > 1) // 2 away
+			{
+				tail.second += (head.second - tail.second) / 2;
+				if(x_diff)
+				{
+					int to_change = std::ceil(std::abs(head.first - tail.first) / 2.0);
+					if(x_diff < 0)
+						tail.first -= to_change;
+					else
+						tail.first += to_change;
+				}
+			}
+
+			visited_positions.insert(tail);
+			// DebugPrint(head, tail, visited_positions);
+			// usleep(1000000);
+		}
+	}
+
+	DebugPrint(head, tail, visited_positions);
+	total = visited_positions.size();
+
+	std::cout << "    Total: " <<     total << std::endl;
+	std::cout << "PT2 Total: " << total_pt2 << std::endl;
+
+	return 0;
+}