Permutations and then sorting in Java

Question

I have a sorting problem.

Let's say I have 4 strings stored in an array, out of these I want to generate all combinations in pairs. And from these pairs sort them so that no 2 array positions get after each other in the greatest extend possible

Example:

String[] array = {"one", "two", "three", "four"};

// want to generate

one - two
one - three
one - four
two - three
two - four
three - four

// then sort

one - two
three - four
one - four
two - three      //two "three" after each other
one - three
two - four

(the one that gets 2 after each other in this case "three" has too be random when sorted)

I have no idea how to do this in Java. Tried nested for loops, some has told me recursive loops. And i don't want:

" Just copy paste this code and everything will work " i really really want to understand how to write something like this.

How should i approach this problem?

Answer 1

Here's your not Just copy paste this code and everything will work : -

Step 1: - Initialize an temp variable to 0 .

Step 2: - Iterate over your array from 0 to arr.length - temp

Step 3: - Print arr[i][temp] - arr[i][i + temp]

Step 4: - Increment temp by 1

Step 5: - Repeat step 2 if temp < arr.length - 1 , as (i + temp) cannot be more than arr.length .

So, for the given array it will print: -

String arr[] = {"one", "two", "three", "four"};

First iteration (Index pair with difference 1) : -

1. arr[0][0] - arr[0][1], then ("one" - "two")
2. arr[0][1] - arr[0][2],      ("two" - "three")
.. so on, 

and then move to next iteration. Increment temp by 1 : -

Second Iteration (Index pair with difference 2) : -

1. arr[0][0] - arr[0][2], then  ("one" - "three")
2. arr[0][1] - arr[0][3]        ("two" - "four")

.. so on.

Last Iteration (Index pair with difference arr.length - 1 ) : -

1. max = arr.length - 1;
2. arr[0][0] - arr[0][max]      ("one" - "four")

So, you can see that, there is nothing as such sorting involved here. If you try to do this with sorting, it will be hell lot of complex.

Answer 2

First come up with an algorithm. it doesn't have to have a particular language set up for it. It's just how you yourself would solve the problem.

Then translate that to the computer.

here's some psudocode to get you started.

public pair[] getPairs(string[] arr)
{

    pair[] retval;
    foreach(string s in arr)
    {
        string first = arr.first
        foreach(string s2 in arr.subArray(allbutfirst))
        {
             retval.Add(newPair(s, s2)
        }
    }
}