Created the advent of code day 3 challenge (part 2)

aoc/03_part_2.cpp

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+#include <iostream>
+#include <fstream>
+#include <vector>
+#include <map>
+
+// Advent of Code 2023, Day 3 Part 2
+
+using namespace std;
+
+int main() {
+    ifstream input("input.txt");
+
+    vector<string> lines;
+
+    for (string line; getline(input, line);) {
+        lines.push_back("." + line + ".");
+    }
+
+    map<string, vector<int>> gears;
+
+    int sum = 0;
+
+    for (int i = 0; i < lines.size(); i++) {
+        string beforeLine = i > 0 ? lines[i - 1] : "";
+        string currentLine = lines[i];
+        string nextLine = i > lines.size() ? "" : lines[i + 1];
+
+        bool buildMode = false;
+        string numberString;
+
+        for (int charIndex = 0; charIndex < currentLine.size(); charIndex++) {
+            char current = currentLine[charIndex];
+
+            if (isdigit(current)) {
+                buildMode = true;
+                numberString.push_back(current);
+                continue;
+            }
+
+            if (buildMode) {
+                cout << "checking " << numberString;
+                int start = charIndex - numberString.size() - 1;
+
+                for (int numSize = start > 0 ? start : 0; numSize <= charIndex; numSize++) {
+                    char currentBelow = i > 0 ? beforeLine[numSize] : '.';
+                    char currentNext = i > lines.size() - 2 && numSize > nextLine.size() ? '.' : nextLine[numSize];
+
+                    bool isInCurrent = (numSize > currentLine.size() ? '.' : currentLine[numSize]) == '*';
+                    bool isInBelow = currentBelow == '*';
+                    bool isInNext = currentNext == '*';
+
+                    if (isInCurrent || isInBelow || isInNext) {
+                        int line =  isInBelow ? i - 1 : isInNext ? i + 1 : i;
+                        string gearId = to_string(line) + "-" + to_string(numSize);
+                        gears[gearId].push_back(stoi(numberString));
+                        cout << " - adding as " << to_string(line) + "-" + to_string(numSize);
+                        break;
+                    }
+                }
+
+                cout << "\n";
+
+                numberString = "";
+                buildMode = false;
+            }
+        }
+    }
+
+    for (const auto &item: gears) {
+        int temp = 1;
+        cout << "SEQUENCE " << item.first << endl;
+        if (item.second.size() != 2) continue;
+        for (const auto &gear: item.second) {
+            temp *= gear;
+            cout << " + " << gear;
+        }
+        cout << "\n";
+        sum += temp;
+    }
+
+    cout << "Sum: " << sum;
+}