Added older advents

advent_of_code_2018/day25/main.cc

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+#include <iostream>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+struct Star
+{
+    int x;
+    int y;
+    int z;
+    int t;
+};
+
+istream& operator>>(istream& in, Star &star)
+{
+    in >> star.x;
+    in.ignore(); //ignore ','
+    in >> star.y;
+    in.ignore();
+    in >> star.z;
+    in.ignore();
+    in >> star.t;
+    in.ignore();
+
+    return in;
+}
+
+ostream &operator<<(ostream &out, Star const &star)
+{
+    out << "[" << star.x << ", " << star.y << ", " << star.z << ", " << star.t << "]";
+    return out;
+}
+
+
+size_t distance(Star const &lhs, Star const &rhs)
+{
+    int dist = abs(lhs.x - rhs.x)
+        + abs(lhs.y - rhs.y)
+        + abs(lhs.z - rhs.z)
+        + abs(lhs.t - rhs.t);
+
+    return dist;
+}
+
+bool in_cluster(vector<Star> const &cluster, Star const &star)
+{
+    for (Star clst : cluster)
+    {
+        if (distance(clst, star) <= 3)
+            return true;
+    }
+
+    return false;
+}
+
+bool same_cluster(vector<Star> const &lhs, vector<Star> const &rhs)
+{
+    for (Star left : lhs)
+    {
+        for (Star right : rhs)
+        {
+            if (distance(left, right) <= 3)
+                return true;
+        }
+    }
+
+    return false;
+}
+
+int main()
+{
+
+    vector<Star> stars;
+
+    while (cin)
+    {
+        Star star;
+        cin >> star;
+        stars.push_back(star);
+    }
+
+    // kickstart 1st cluster
+    vector<vector<Star>> clusters;
+    
+    for (Star star : stars)
+    {
+        bool matched = false;
+
+        for (vector<Star> &cluster : clusters)
+        {
+            if (in_cluster(cluster, star))
+            {
+                cluster.push_back(star);
+                matched = true;
+                break;
+            }
+        }
+
+        if (!matched)
+        {
+            clusters.push_back({});
+            clusters.back().push_back(star);
+        }
+    }
+
+    bool merged = true;
+    while (merged)
+    {
+        merged = false;
+        for (size_t idx = 0; idx < clusters.size(); ++idx)
+        {
+            for (size_t jdx = idx + 1; jdx < clusters.size(); ++jdx)
+            {
+                if (same_cluster(clusters[idx], clusters[jdx]))
+                {
+                    clusters[idx].insert(clusters[idx].end(), clusters[jdx].begin(), clusters[jdx].end());
+                    clusters.erase(clusters.begin() + jdx);
+                    merged = true;
+                    break;
+                }
+            }
+            if (merged) break;
+        }
+    }
+
+    for (vector<Star> cluster : clusters)
+    {
+        cout << "\n\nCluster:\n";
+        for (Star star : cluster)
+        {
+            cout << "    Star: " << star << "\n";
+        }
+    }
+
+    cout << "Num clusters: " << clusters.size() << "\n";
+}