Day 12 - Part 2

Day12/Day12.cs

@@ -29,16 +29,36 @@ namespace Advent
 
             public Coordinates Position { get; }
             public Coordinates Velocity { get; }
+
+            public string GetState()
+            {
+                return $"{Position.Z},{Velocity.Z}";
+            }
         }
 
         public static void Execute()
         {
+            /*
+                <x=-1, y=0, z=2>
+                <x=2, y=-10, z=-7>
+                <x=4, y=-8, z=8>
+                <x=3, y=5, z=-1>
+            */
+
+            //var moons = new List<Moon>
+            //{
+            //    new Moon(-1, 0, 2) ,
+            //    new Moon(2, -10, -7),
+            //    new Moon(4,  -8, 8 ),
+            //    new Moon(3, 5,  -1 )
+            //};
+
             /*
                 <x=-4, y=-9, z=-3>
                 <x=-13, y=-11, z=0>
                 <x=-17, y=-7, z=15>
                 <x=-16, y=4, z=2>
-             */
+            */
 
             var moons = new List<Moon>
             {
@@ -48,7 +68,14 @@ namespace Advent
                 new Moon(-16, 4,  2 )
             };
 
-            for (var count = 1; count <= 1000; count++)
+            //Console.WriteLine(lcm_of_array_elements(new long[] { 113028, 167624, 231614 }));
+            //return;
+
+            var previousStates = new Dictionary<string, int>();
+
+            var index = 1;
+
+            while (true)
             {
                 for (var a = 0; a <= 3; a++)
                 {
@@ -98,19 +125,98 @@ namespace Advent
                     moon.Position.Y += moon.Velocity.Y;
                     moon.Position.Z += moon.Velocity.Z;
                 }
+
+                var states = new List<string>();
+
+                foreach (var moon in moons)
+                    states.Add(moon.GetState());
+
+                var totalState = string.Join(':', states.ToArray());
+
+                if (previousStates.ContainsKey(totalState))
+                {
+                    Console.WriteLine(index - previousStates[totalState]);
+                    break;
+                }
+                else
+                {
+                    previousStates[totalState] = index++;
+                }
             }
 
-            var totalEnergy = 0;
+            //var totalEnergy = 0;
 
-            foreach (var moon in moons)
+            //foreach (var moon in moons)
+            //{
+            //    var potentialEnergy = Math.Abs(moon.Position.X) + Math.Abs(moon.Position.Y) + Math.Abs(moon.Position.Z);
+            //    var kineticEnergy = Math.Abs(moon.Velocity.X) + Math.Abs(moon.Velocity.Y) + Math.Abs(moon.Velocity.Z);
+
+            //    totalEnergy += (potentialEnergy * kineticEnergy);
+            //}
+
+            //Console.WriteLine(totalEnergy);
+        }
+
+        private static long lcm_of_array_elements(long[] element_array)
+        {
+            long lcm_of_array_elements = 1;
+            int divisor = 2;
+
+            while (true)
             {
-                var potentialEnergy = Math.Abs(moon.Position.X) + Math.Abs(moon.Position.Y) + Math.Abs(moon.Position.Z);
-                var kineticEnergy = Math.Abs(moon.Velocity.X) + Math.Abs(moon.Velocity.Y) + Math.Abs(moon.Velocity.Z);
 
-                totalEnergy += (potentialEnergy * kineticEnergy);
+                int counter = 0;
+                bool divisible = false;
+                for (int i = 0; i < element_array.Length; i++)
+                {
+
+                    // lcm_of_array_elements (n1, n2, ... 0) = 0. 
+                    // For negative number we convert into 
+                    // positive and calculate lcm_of_array_elements. 
+                    if (element_array[i] == 0)
+                    {
+                        return 0;
+                    }
+                    else if (element_array[i] < 0)
+                    {
+                        element_array[i] = element_array[i] * (-1);
+                    }
+                    if (element_array[i] == 1)
+                    {
+                        counter++;
+                    }
+
+                    // Divide element_array by devisor if complete 
+                    // division i.e. without remainder then replace 
+                    // number with quotient; used for find next factor 
+                    if (element_array[i] % divisor == 0)
+                    {
+                        divisible = true;
+                        element_array[i] = element_array[i] / divisor;
+                    }
+                }
+
+                // If divisor able to completely divide any number 
+                // from array multiply with lcm_of_array_elements 
+                // and store into lcm_of_array_elements and continue 
+                // to same divisor for next factor finding. 
+                // else increment divisor 
+                if (divisible)
+                {
+                    lcm_of_array_elements = lcm_of_array_elements * divisor;
+                }
+                else
+                {
+                    divisor++;
+                }
+
+                // Check if all element_array is 1 indicate  
+                // we found all factors and terminate while loop. 
+                if (counter == element_array.Length)
+                {
+                    return lcm_of_array_elements;
+                }
             }
-
-            Console.WriteLine(totalEnergy);
         }
     }
 }