Finish with simulated annealing search

using System;

namespace SA
{
	
	class Ball
	{
		public readonly int targetIndex;
		public readonly string id;
		public Ball(string id, int targetIndex)
		{
			this.id = id;
			this.targetIndex = targetIndex;
		}
		
		public int energy( int index)
		{ 
			int d = (targetIndex-index)*2;
			
			int e = d*d; // 'basic' enrgy: squared distance from target index
			
			if ( targetIndex < 3 )
			{
				if ( index >= 3)
					e += 1000;  // sum a noticeable energy when 'on the wrong side'
			}
			else if ( targetIndex == 3)
			{
				e += d*d*d*d*1000; // sum big energy if the gap is in wrong position
			}
			else	
			{
				if ( index <= 3)
					e += 1000; // sum a noticeable energy when 'on the wrong side'
			}
			return e;
		}
	}
	
	class Test
	{
		
		static int energy( Ball [] ball)
		{
			int e = 0;
			for (int n=0; n< ball.Length; ++n)
			{
				e += ball[n].energy(n);
			}
			return e;
		}
		
		static double probability(int energy, double temperature)
		{
			if (energy <=0) return 1.0;
			double p = Math.Exp(-(double)energy/temperature);
			return p;
		}
		
		static void dump( Ball [] ball, int energy, double temperature)
		{
			foreach (var b in ball)
			{
				Console.Write("{0} ", b.id);
			}
			Console.WriteLine("{0} {1}", energy, temperature);
		}
		
		// Driver method 
		public static void Main() 
		{
			const double THot=300000;
			const double TCold=30000;
			const double TSub=2.0;
			double t = THot;
			Random rnd = new Random();
			
			Ball [] ball = new Ball[8];
			ball[0] = new Ball("B1", 4);
			ball[1] = new Ball("B2", 5);
			ball[2] = new Ball("B3", 6);
			ball[3] = new Ball("B4", 7);
			ball[4] = new Ball("GP", 3);
			ball[5] = new Ball("W1", 0);
			ball[6] = new Ball("W2", 1);
			ball[7] = new Ball("W3", 2);
			
			int cur_gp_index = 4;
			int cur_energy = energy(ball);
			
			while ( t > TCold)
			{
				const int Iterations = 250;
				for (int n=0; n<Iterations; ++n)
				{
					int new_gp_index;
					int new_energy;
					for (;;)
					{
						int r = rnd.Next(-2,3); // <- Fixed a blunder, thanks to Luc Pattyn
						new_gp_index = cur_gp_index + r;
						if ( new_gp_index != cur_gp_index && new_gp_index >=0 && new_gp_index<=7)
							break;
					}
					// swap
					Ball temp = ball[new_gp_index];
					ball[new_gp_index] = ball[cur_gp_index];
					ball[cur_gp_index] = temp;
					new_energy = energy(ball);
					if ( probability( new_energy - cur_energy, t) > .95)
					{
						//dump (ball, new_energy, t);
						cur_energy=new_energy;
						cur_gp_index = new_gp_index;
					}
					else
					{
						temp = ball[new_gp_index];
						ball[new_gp_index] = ball[cur_gp_index];
						ball[cur_gp_index] = temp;
					}
				}
				t-=TSub;
			}
			dump (ball, cur_energy, t);
			Console.WriteLine("done.");
			Console.ReadLine();
		} 
	}
}