Sorting matched arrays in Java

Question

Let's say that I have two arrays (in Java),

int[] numbers; and int[] colors;

Each ith element of numbers corresponds to its ith element in colors. Ex, numbers = {4,2,1} colors = {0x11, 0x24, 0x01}; Means that number 4 is color 0x11, number 2 is 0x24, etc.

I want to sort the numbers array, but then still have it so each element matches up with its pair in colors.

Ex. numbers = {1,2,4}; colors = {0x01,0x24,0x11};

What's the cleanest, simplest way to do this? The arrays have a few thousand items, so being in place would be best, but not required. Would it make sense to do an Arrays.sort() and a custom comparator? Using library functions as much as possible is preferable.

Note: I know the "best" solution is to make a class for the two elements and use a custom comparator. This question is meant to ask people for the quickest way to code this. Imagine being at a programming competition, you wouldn't want to be making all these extra classes, anonymous classes for the comparator, etc. Better yet, forget Java; how would you code it in C?

Answer 1

You could use sort() with a custom comparator if you kept a third array with the index, and sorted on that, leaving the data intact.

Java code example:

Integer[] idx = new Integer[numbers.length]; for( int i = 0 ; i < idx.length; i++ ) idx[i] = i;               Arrays.sort(idx, new Comparator<Integer>() {     public int compare(Integer i1, Integer i2) {                                 return Double.compare(numbers[i1], numbers[i2]);     }                    });  // numbers[idx[i]] is the sorted number at index i // colors[idx[i]] is the sorted color at index i 

Note that you have to use Integer instead of int or you can't use a custom comparator.

Answer 2

It seems like the cleanest thing to do would be to create a custom property class that implements Comparable. For example:

class Color implements Comparable {   private int number;   private int color;    // (snip ctor, setters, etc.)    public int getNumber() {     return number;   }   public int getColor() {     return color;   }    public int compareTo(Color other) {     if (this.getNumber() == other.getNumber) {       return 0;     } else if (this.getNumber() > other.getNumber) {       return 1;     } else {       return -1;     }   } } 

Then you can separate your sorting algorithm from the ordering logic (you could use Collections.sort if you use a List instead of an array), and most importantly, you won't have to worry about somehow getting two arrays out of sync.