2 opt for TSP.
The seed solution is global, in sol[]

      private void Loc2opt()  // 2-opt
      {  int i,j,temp,cost1,cost2,i1,i2,j1,j2,DeltaMax,imax,jmax;

start:   DeltaMax=imax=jmax=0;
         for(i=0;i<n;i++)
            for(j=i+1;j<n;j++)
            {  //i=rnd.Next(0,n);
               //j=rnd.Next(0,n);
               cost1=cost2=0;
               i1=(i==0 ? n-1 : i-1); // ind. di chi precede i
               i2=(i==n-1 ? 0 : i+1); // ind. di chi segue i
               j1=(j==0 ? n-1 : j-1); // ind. di chi precede j
               j2=(j==n-1 ? 0 : j+1); // ind. di chi segue j
               if((j-i)>1 && (j-i)<(n-1))
               {  cost1=d[sol[i1],sol[i]]+d[sol[i],sol[i2]]+d[sol[j1],sol[j]]+d[sol[j],sol[j2]];
                  cost2=d[sol[i1],sol[j]]+d[sol[j],sol[i2]]+d[sol[j1],sol[i]]+d[sol[i],sol[j2]];
               }
               else if((j-i)==1)
               {  cost1=d[sol[i1],sol[i]]+d[sol[i],sol[j]]+d[sol[j],sol[j2]];
                  cost2=d[sol[i1],sol[j]]+d[sol[j],sol[i]]+d[sol[i],sol[j2]];
               }
               else if((j-i)==(n-1))
               {  cost1=d[sol[j1],sol[j]]+d[sol[j],sol[i]]+d[sol[i],sol[i2]];
                  cost2=d[sol[j1],sol[i]]+d[sol[i],sol[j]]+d[sol[j],sol[i2]];
               }
               if(cost1-cost2>DeltaMax)
               {  DeltaMax=cost1-cost2;
                  imax=i;
                  jmax=j;
               }
            }
         if(DeltaMax>0)
         {  temp=sol[imax];
            sol[imax]=sol[jmax];
            sol[jmax]=temp;
            // MessageBox.Show(this.label1,"Scambio "+sol[imax].ToString()+" "+sol[jmax].ToString());
            goto start;
         }
     }