09

2022/09/Makefile

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+CXX ?= c++
+CXXFLAGS ?= -std=c++11 -Wall -Wextra -pedantic -O2
+PROJECT = rope_simulator
+
+all: ${PROJECT}
+
+${PROJECT}: main.cpp
+	${CXX} ${CXXFLAGS} -o $@ $^
+
+test: ${PROJECT}
+	./${PROJECT}
+
+clean:
+	${RM} *.o ${PROJECT}
+
+.PHONY: all clean test

2022/09/main.cpp

@@ -0,0 +1,123 @@
+#include <fstream>
+#include <iostream>
+#include <sstream>
+#include <vector>
+#include <unordered_map>
+
+enum Directions {
+    UP,
+    DOWN,
+    LEFT,
+    RIGHT
+};
+
+struct Command {
+    Directions direction;
+    int steps;
+};
+
+struct Position {
+    int x;
+    int y;
+};
+
+Directions charToDirection(char c) {
+    switch(c) {
+        case 'R':
+            return RIGHT;
+        case 'L':
+            return LEFT;
+        case 'U':
+            return UP;
+        case 'D':
+            return DOWN;
+    }
+    std::cerr << "Invalid direction" << std::endl;
+    exit(1);
+}
+
+std::vector<Command> getCommands( std::ifstream &file ) {
+    std::vector<Command> ret{};
+    int tmp_i = 0;
+    char tmp_c = 0;
+    std::string str;
+    while ( std::getline( file, str ) ) {
+        std::stringstream ss( str );
+        ss >> tmp_c;
+        ss >> tmp_i;
+        ret.push_back({charToDirection(tmp_c), tmp_i});
+    }
+    return ret;
+}
+
+void handleMovement(const Position &head, Position &tail) {
+    auto x_diff = head.x - tail.x;
+    auto y_diff = head.y - tail.y;
+    if(abs(x_diff) > 1 || abs(y_diff) > 1) {
+        if(x_diff != 0) {
+            x_diff /= abs(x_diff);
+        }
+        if(y_diff != 0) {
+            y_diff /= abs(y_diff);
+        }
+        tail.x += x_diff;
+        tail.y += y_diff;
+    }
+}
+
+int ropeSimulation(const std::vector<Command> &commands, int rope_length) {
+    std::vector<Position> positions;
+    positions.resize(rope_length);
+    for(int i = 0; i < rope_length; i++) {
+        positions[i] = {0, 0};
+    }
+    std::unordered_map<int, std::unordered_map<int, bool>> visits{};
+    visits[0][0] = true;
+    for(auto &command : commands) {
+        Position addition{0, 0};
+        switch(command.direction) {
+            case RIGHT:
+                addition = {1, 0};
+                break;
+            case LEFT:
+                addition = {-1, 0};
+                break;
+            case UP:
+                addition = {0, -1};
+                break;
+            case DOWN:
+                addition = {0, 1};
+                break;
+        }
+        for(int i = 0; i < command.steps; i++) {
+            positions[0].x += addition.x;
+            positions[0].y += addition.y;
+            for(int i = 1; i < rope_length; i++) {
+                handleMovement(positions[i-1], positions[i]);
+            }
+            visits[positions.back().x][positions.back().y] = true;
+        }
+    }
+    int result = 0;
+    for(auto &visit : visits) {
+        result += visit.second.size();
+    }
+    return result;
+}
+
+int part1(const std::vector<Command> &commands) {
+    return ropeSimulation(commands, 2);
+}
+
+int part2(const std::vector<Command> &commands) {
+    return ropeSimulation(commands, 10);
+}
+
+int main() {
+    std::ifstream input_file( "input" );
+    auto commands = getCommands( input_file );
+    std::cout << "The rope's tail visits \033[91;1m" << part1(commands)
+              << "\033[0m positions." << std::endl;
+    std::cout << "The long rope's tail visits \033[91;1m" << part2(commands)
+              << "\033[0m positions." << std::endl;
+}