Rearranging numbers of an array like a wave

Question

Given an array of integers, sort the array into a wave like array and return it, In other words, arrange the elements into a sequence such that a1 >= a2 <= a3 >= a4 <= a5.....

Example

Given [1, 2, 3, 4]

One possible answer: [2, 1, 4, 3]
Another possible answer : [4, 1, 3, 2]

NOTE: If there are multiple answers possible, return the one thats lexicographically smallest. So, in example case, you will return [2, 1, 4, 3]

My approach:

public class Solution {
    public ArrayList<Integer> wave(ArrayList<Integer> A) {

        Collections.sort(A);
        int swap1, swap2,temp1,temp2;
        //We will have to swap all the odd numbered elements with the even numbered elements
        //such that all numbers with a gap 0f 1 are sorted
        for( swap1= 0, swap2 = swap1 + 1; swap1 <= A.size()- 2; swap1 = swap1+2,swap2 = swap2+2 )
            {
                //Check if swap1 reaches last element
                if( (swap1 == A.size() - 1) || (swap2 == A.size()) )
                    break;
                else
                    {
                        temp1 = A.get(swap1);
                        temp2 = A.get(swap2);
                        A.set(swap1,temp2);
                        A.set(swap2, temp1);
                    }
            }
        return A;
    }
}

I have the following questions regarding my code:

1. How can I further optimize my code? (I am unable to solve these questions within the prescribed time limit. What can I do?)

2. Is there any better approach to do this question?

3. Have I violated any convention in coding?

4. Are there any redundancies in my approach?

Reference

Answer 1

Few observations.

1. You don't need to maintain swap2 separately, it is always swap1 + 1, so can be simply declared inside the loop's body.

2. Your boundaries check inside the loop body is redundant, loop condition alone is enough.

3. You're probably performing too many int-to-Integer and back conversions. Even more, the question deals with arrays, you don't need to pre-convert the argument into a list. Accept, process and return an array of plain ints.