网捷达

Given an integer array, sort its elements in ascending order while retaining and displaying their original indexes, ensuring the initial positions of elements are preserved after sorting.

Examples:

Input: arr[] = {20, 40, 30, 10}
Output:
Element | Original index
10 | 3
20 | 0
30 | 2
40 | 1

Approach

Follow these steps to sort the array while keeping track of original indexes:

Define a class ArrItem to store each element and its original index.
Create an ArrayList of ArrItem objects from the array elements.
Sort the list using Collections.sort() with a custom comparator based on the element value.
Traverse the sorted list and print each element along with its original index.

Implementation

Java

import java.util.*;

class ArrItem {
    int item;
    int index;

    ArrItem(int im, int ix) {
        item = im;
        index = ix;
    }
}

class MyCmp implements Comparator<ArrItem> {
    public int compare(ArrItem i1, ArrItem i2) {
        
        // Sort by element value
        return i1.item - i2.item; 
    }
}

class GfG {

    static void printSortedWithIndexes(int arr[]) {
        int n = arr.length;
        ArrayList<ArrItem> list = new ArrayList<>(n);

        // Store elements with their original indexes
        for (int i = 0; i < n; i++) {
            list.add(new ArrItem(arr[i], i));
        }

        // Sort the list based on element values
        Collections.sort(list, new MyCmp());

        // Print elements along with their original indexes
        for (ArrItem x : list) {
            System.out.println(x.item + " " + x.index);
        }
    }

    public static void main(String args[]) {
        int arr[] = { 20, 10, 5, 4 };
        printSortedWithIndexes(arr);
    }
}

Output

Keeping indexes after sorting in Java

Approach

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