包含数字的字符串排序数组

Question

I have an interview exercise today:

return A sorted array (case insensitive). A sorted array will be sorted

 * alphabetically by the first 3 characters, then numerically by 
 * the following number and then alphabetically by the remaining characters with
 * spaces above characters.


import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;

import org.junit.Test;

public class MySort {


    public String[] testSortArray(String[] input){
        // TODO: Sort the array

    }

    @Test
    public void testSort() {
        String[] input = new String[8];
        input[0] = "AIR1";
        input[1] = "AIR20b";
        input[2] = "BIR5A";
        input[3] = "AIR20AB";
        input[4] = "AIR10ab";
        input[5] = "AIR2 A";
        input[6] = "AIR111";
        input[7] = "AIR1Z";

        MySort sortTest = new MySort();
        String[] output = sortTest.testSortArray(input);

        String[] expected = new String[8];
        expected[0] = "AIR1";
        expected[1] = "AIR1Z";
        expected[2] = "AIR2 A";
        expected[3] = "AIR10ab";
        expected[4] = "AIR20AB";
        expected[5] = "AIR20b";
        expected[6] = "AIR111";
        expected[7] = "BIR5A";
        assertEquals(Arrays.asList(output), Arrays.asList(expected));

        for (String item : output) {
            System.out.println(item);
        }
    }
}

I have implemented testSortArray(String[] input as :

public String[] testSortArray(String[] input){

        Collections.sort(Arrays.asList(input), new Comparator<String>() {
            public int compare(String o1, String o2) {
                return extractNumber(o1) - extractNumber(o2);
            }

            int extractNumber(String s) {
                String num = s.replaceAll("\\D", "");
                // return 0 if no digits found
                return num.isEmpty() ? 0 : Integer.parseInt(num);
            }
        });
        return input;
    }

Can you please tell me what's wrong in my code ? thanks

Answer 1

Your comparison logic obviously doesn't come close to matching your spec. It completely ignores the first three characters, and ignores everything after the digit after the first three characters. Clearly you need to take these things into consideration or you can never match your spec:

    public int compare(String o1, String o2) {
            String s1 = o1.substring(0, 3);
            String s2 = o2.substring(0, 3);
            if(!s1.equals(s2)) {
                return s1.compareTo(s2);
            }
            String[] fields1 = o1.substring(3).split("[^0-9]", 2);
            String[] fields2 = o2.substring(3).split("[^0-9]", 2);
            int i1 = Integer.parseInt(fields1[0]);
            int i2 = Integer.parseInt(fields2[0]);
            if(i1 != i2) {
                return i1 - i2;
            }
            String r1 = "";
            if(fields1.length > 1) {
                r1 = fields1[1];
            }
            String r2 = "";
            if(fields2.length > 1) {
                r2 = fields2[1];
            }
            return r1.compareTo(r2);
        }

This will match your spec. I tested an obtained the following output:

AIR1
AIR1Z
AIR2 A
AIR10ab
AIR20AB
AIR20b
AIR111
BIR5A