Traveling Salesman for java

Question

Based on this pseudo code I am trying to implement a java fittness function for the Traveling Salesman problem but I am not sure if I am doing it right, can someone please help me out.

N   The number of cities to visit
T   A tour (list of integers of size N)
D   An N by N matrix containing each d(i,j)

Let s = 0
For i = 1 to (N-1)
Let a = ti
Let b = ti+1
Let s = s + d(a,b)
 End For
     Let end_city = tn
     Let start_city = t1
     Let s = s + d(end_city,start_city)
The tour length s

My attempt at writing this in java

public static ArrayList<Integer> Fitness(){
    int n = 10; // Number of cities to visit
    ArrayList<Integer> t = new ArrayList<Integer>();
    int[][] d = null;
    int s = 0, a, b;

    for (int i = 1; i<n; i++){
        for (int j = 1; j<n; j++){
            d = new int[i][j];
        }

        for( i = 1; i<n; i++){
            a = t.get(i);
            b = t.get(i+1);
            s = s + d[a][b];
        }
        int end_city = t.get(n);
        int start_city = t.get(1);
        s = s + d[end_city][start_city];
    }
    return t;

Can someone please help me out. Thanks.

Answer 1

You should start be deciding what you have and what you want.

---

What you have

For a fitness function for Travelling Salesman Problem, according to your pseudo-code, you will have following input.

• Number of cities
• A tour whose fitness is to be calculated
• Map with distances (in this case adjacency matrix).

This should be the formal parameters of your fitness function.

---

What you want

The purpose of a fitness function is to have a way to measure quality in terms of a single parameter.

In this case, the length is serving that purpose.

This should be the returning value of your fitness function.

---

This makes the prototype of your fitness function to be as following

public double fitness(List<Integer> tour,
                      int numberOfCities,
                      double[][] distanceBetween);

---

Now the pseudo-code for the body is easy to decode if you indent it correctly and have another look.

Let s = 0
For i = 1 to (N-1)
    Let a = ti
    Let b = ti+1
    Let s = s + d(a,b)
End For
Let end_city = tn
Let start_city = t1
Let s = s + d(end_city,start_city)
The tour length s

It should be fairly easy to work out the rest. It is pretty straightforward to translate it to Java.

Good luck.