java - Sorting an array of int in lexicographic order

Question

I came across a problem such that:

WAP to sort prime numbers smaller than given N by digits. If N is 40, the output should be 11, 13, 17, 19, 2, 23, 29, 3, 31, 37, 39, 5, 7. Note: Limit memory use.

Getting primary number was the easy. But I could not figure out an efficient way of lexicographic sorting of array of integer.

public static void getPrimeNumbers(int limit) {
        for (int i=2; i<=limit; i++) {
            if(isPrime(i)) {
                System.out.println(i);
            }
        }
    }

    public static boolean isPrime(int number) {
        for(int j=2; j<number; j++) {
            if(number%j==0) {
                return false;
            }
        }
            return true;
    }

    public static void lexographicSorting() {
        int[] input = {2,3,5,7,11,13,17,19};
        int[] output = {};
        for (int i=0; i<input.length; i++) {
            for(int j=0; j<input.length; j++) {
                ////Stuck at this part.
            }
        }
    }

Answer 1

Java String#compareTo already implements this functionality, you can access it pretty easily by converting your Integer objects to String objects and calling compareTo

Arrays.sort(input, new Comparator<Integer>() {
   @Override
   int compareTo( Integer x, Integer y ) {
      return x.toString().compareTo( y.toString() );
   }
};

I can say exactly how memory efficient this would be, you have to create 1 Integer object for each primitive int in your array, then you have to create 1 String object for each Integer object you have. So there is probably a good deal of overhead in object creation.