how can i store the original index of an int array in sorted form?

Question

i want to store the original index numbers of array elements before for sorting in ascending order.

assume if the elements in array are

x[]= {20,40,70,80,50,30};

i want another array to return with index number of the sorted form like

sorted[] = {0,5,1,4,2,3}

i tried many times. but can't figure out how to get the index numbers. everytime the index number gets changed after the swap.

Note:

i can't use comparotor,map,Arrays.sort or anything like that. i have to use loop only.

i already searched all the websites. i cant find any specific answer. cause all of them uses comparator map or something that i am not allowed to use at the moment.

public static int[] sort(int[] numbers) {
    int[] sorted = new int[numbers.length];
    int temp;
    int[] index= new int[numbers.length];
    for (int i = 0; i < numbers.length; i++) {
        for (int j = i+1; j < numbers.length; j++) {
            if (numbers[i] > numbers[j]) {
                temp = numbers[i];
                numbers[i] = numbers[j];
                numbers[j] = temp;
                index[i]= j;
            }
        }
    }
    return index;
}

What about storing the indexes before sorting and constructing the sortedIndexes array after? — RubioRic, Feb 16 '18 at 09:37
Possible duplicate of [How to get indices of a sorted array in Python](https://stackoverflow.com/questions/6422700/how-to-get-indices-of-a-sorted-array-in-python) — F0XS, Feb 16 '18 at 09:38
Make an array of indices `{ 0, 1, 2, 3, 4, 5 }`. Sort it the way you already sort, only instead of comparing `indices[i]` and `indices[j]` compare `numbers[indices[i]]` and `numbers[indices[j]]`. — Ole V.V., Feb 16 '18 at 09:56
You shouldn’t post your answer or your “Thank you” in your question. They are already in your answer, that’s where they belong (if not just in a comment). It’s easier to navigate on Stack Overflow when we use the fields as intended. — Ole V.V., Feb 16 '18 at 12:35

score 1 · Accepted Answer · answered Feb 16 '18 at 10:40

1

i was able to do it by storing the original array in another array and then use loop to compare the sorted array and store the index .

Thanks @RubioRic @RCInd .

answered Feb 16 '18 at 10:40

niklaus

21
6

score 0 · Answer 2 · edited Jun 20 '20 at 09:12

I think this is what you're looking for:

keep positions in a map

Sort

Lookup the map for the indexes before the sorting PS: The complexity would come because of the duplicates. You need to handle that with the help of another map

See the working code here...

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.print.attribute.HashAttributeSet;

public class PositionFinder{


    public static void main(String[] args) {
        Integer []a = {3,2,3,0,1};
        Map <Integer , List<Integer>> map = new HashMap<>();

        for (int i = 0; i < a.length; i++) {
            int j = a[i];
            if(map.get(j)==null){
                map.put(j, new ArrayList<>());
                map.get(j).add(i);
            }
            else{
                map.get(j).add(i);
            }
        }

        System.out.println("Positions ->" + map);

        //sort
        List<Integer> l = new ArrayList<Integer>(Arrays.asList(a));

        Collections.sort(l);

        System.out.println("Sorted List -->" + l );


        //get and print index
        List positionList = new ArrayList<>();
        Map<Integer, Integer> duplicateTrackerMap = new HashMap<>();
        for (Integer key : l) {
            int pos = 0;
            if(duplicateTrackerMap.get(key) != null){
                pos = 1+ duplicateTrackerMap.get(key);

            }
            duplicateTrackerMap.put(key, pos);
            positionList.add(map.get(key).get(pos));
        }
        System.out.println("Sort index -->" +  positionList);
    }


}

create a copy of the array and carry on with what is done here using map — RCInd, Feb 16 '18 at 10:15

score 0 · Answer 3 · answered Feb 16 '18 at 10:52

    int x[] = { 20, 40, 70, 80, 50, 30 };
    int[] array = new int[x.length];
    for (int i = 0; i < x.length; i++) {
        array[i] = i;
    }
    for (int i = (x.length - 1); i >= 0; i--) {
        for (int j = 1; j <= i; j++) {
            int oneMi = j - 1;
            if (x[oneMi] > x[j]) {
                int temp = x[oneMi];
                x[oneMi] = x[j];
                x[j] = temp;
                int swi = array[oneMi];
                array[oneMi] = array[j];
                array[j] = swi;
            }
        }
    }

    for (int i = 0; i < array.length; i++) {
        System.out.println(array[i]);
    }

how can i store the original index of an int array in sorted form?

3 Answers3