How can I sort a 2D array and keep track of the original indexes in Java

Question

I have a 2D array called distance[][]

It holds my values in column 0:

Example:

{ 5
  7
  3
  9 }

It seems like a 1D array, however I've converted it into a 2D array in order to be able to keep track of my indexes.

The way I access my first value is distance[0][0].

My question is: how can I keep track of the original index positions if I were to sort my array. I was under the impression that I may need to create a corresponding list of numbers in ascending order which correspond with the position my of distance values.

What would I do after that?

Answer 1

最简单的解决方案是创建一个包含该项目及其对应索引的Pair类，然后将这个Pair类的列表保留在两个不同的list而不是对其中的一个进行排序。因为在Java中，您可以使用引用而不创建复制对象，这应该很容易。现在排序列表将包含值和根据值排序的相应索引，而未排序列表将按照您输入的顺序Pair ，即根据索引排序。

Answer 2

All you need is to use comparator. Consider below code -

Arrays.sort(arr, new java.util.Comparator<int[]>(){
    public int compare(int[] a,int[] b){
        return a[0]-b[0];
    }
});

arr is your orginial 2d array, where first column contains the number to sorted and second column contains index