Added older advents

advent_of_code_2015/day3/main2.cc

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+#include <iostream>
+#include <set>
+#include <string>
+
+using namespace std;
+
+class Point
+{
+    public:
+        int x;
+        int y;
+};
+
+
+bool operator<(Point const &lhs, Point const &rhs)
+{
+    if (lhs.x == rhs.x)
+        return lhs.y < rhs.y;
+    return lhs.x < rhs.x;
+}
+
+int main()
+{
+    bool robo = false;
+    set<Point> delivered;
+    Point position{0, 0};
+    Point robo_position{0, 0};
+    delivered.insert(position);
+
+    while (!cin.eof())
+    {
+        switch (cin.get())
+        {
+            case '>': 
+                ++(robo ? robo_position : position).x;
+            break;
+
+            case '<':
+                --(robo ? robo_position : position).x;
+            break;
+
+            case '^':
+                --(robo ? robo_position : position).y;
+            break;
+
+            case 'v':
+                ++(robo ? robo_position : position).y;
+            break;
+        }
+
+        robo = !robo;
+        delivered.insert(robo ? robo_position : position);
+    }
+
+    cout << "Delivered count: " << delivered.size() << "\n";
+}