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

Looking at the example {5,54,56}, the proper way to order these numbers is when comparing strings A and B, we should consider lexicographic ordering of A+B with B+A.

For example:

• Comparing (5,54) becomes lexicographic comparison of ("554" with "545")
• Comparing (5,56) becomes lexicographic comparison of ("556" with "565")
• Comparing (54,56) becomes lexicographic comparison of ("5456" with "5654")

If we sort them this way, the resulting array is {56,5,54}.

Here's a Java implementation of this idea:

public class LexicographicSort implements Comparator {

    public int compare(Integer o1, Integer o2) {
        String s1 = o1.toString();
        String s2 = o2.toString();
        return (s2+s1).compareTo(s1+s2);
    }

    public static void main(String[] args) {
        LexicographicSort ls = new LexicographicSort();
        Integer[] nums = {9,1,95,17,5};
        Arrays.sort(nums, ls);
        System.out.println(Arrays.toString(nums));
    }
}