How can I manipulate an array to make the largest number?

Question

Say you have an array of positive integers, manipulate them so that the concatenation of the integers of the resultant array is the largest number possible. Ex: {9,1,95,17,5}, r

Answer 1

The idea of @Nate Kohl is very good. I just implemented a Java version using quicksort. Here it is:

import java.util.Random;

public class Sort_MaxConcatenation {
    private Random r = new Random();

    public void quicksort_maxConcatenation(int[] a, int begin, int end) {
        if (begin < end) {
            int q = partition(a, begin, end);
            quicksort_maxConcatenation(a, begin, q);
            quicksort_maxConcatenation(a, q + 1, end);
        }
    }

    private int partition(int[] a, int begin, int end) {
        int p = begin + r.nextInt(end - begin + 1);
        int t1 = a[p];
        a[p] = a[end];
        a[end] = t1;

        int pivot = t1;
        int q = begin;
        for (int i = begin; i < end; i++) {
            if (compare_maxConcatenation(a[i], pivot) > 0) {
                int t2 = a[q];
                a[q] = a[i];
                a[i] = t2;
                q++;
            }
        }
        int t3 = a[q];
        a[q] = a[end];
        a[end] = t3;

        return q;
    }

    private int compare_maxConcatenation(int i, int j) {
        int ij = Integer.valueOf(String.valueOf(i).concat(String.valueOf(j)));
        int ji = Integer.valueOf(String.valueOf(j).concat(String.valueOf(i)));
        if (ij > ji)
            return 1;
        else if (ij == ji)
            return 0;
        return -1;
    }

    public static void main(String[] args) {

        int[] a = new int[]{56, 5, 4, 94, 9, 14, 1};
        Sort_MaxConcatenation smc = new Sort_MaxConcatenation();
        smc.quicksort_maxConcatenation(a, 0, a.length-1);
        for(int i = 0;i < a.length;i++) {
            System.out.print(a[i]);
        }
    }
}