How to Sort an Array by Odd and Even Numbers Separately in Java

Learn how to sort an array where odd and even numbers are arranged separately in descending and ascending order respectively using Java.
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Introduction

Sorting an array can be straightforward, but sometimes we have specific requirements that complicate things. For example, you might want to sort the numbers in such a way that all even numbers are in ascending order, while all odd numbers are in descending order—but still maintain their original positions.

In our scenario, we start with the array [3, 4, 5, 1, 2] and we want to achieve the output [5, 2, 3, 1, 4]. Here we will explore how to implement this using Java, breaking down the problem step-by-step.

Understanding the Problem

Given the input array:

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The expected output is:

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Breakdown of the Requirements

Odd Numbers:

From the input array, the odd numbers are [3, 5, 1].

These should be arranged in descending order, resulting in [5, 3, 1].

Even Numbers:

The even numbers from the input array are [4, 2].

These should be arranged in ascending order, resulting in [2, 4].

Maintaining Positions:

The odd numbers must take their original positions among the indices where they were found in the input, while even numbers maintain theirs.

Steps to Sort the Array

Step 1: Initialize the Data Structures

To achieve the desired sorting, we can start by creating a method that separates odd and even numbers while storing their positions.

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Step 2: Populate the Lists

Loop through the input array to populate our odd and even lists based on whether the number is odd or even.

Step 3: Sort the Lists

Sorting Odds Descending:
You can use a nested loop to compare and swap odd numbers.

Sorting Evens Ascending:
Similarly, use another loop for even numbers.

Here’s the snippet to sort the odds and evens:

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Step 4: Reconstruct the Output

Now that we have our sorted arrays, we can reconstruct the final array using the indices of the original array.

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Conclusion

With the above code, you can successfully sort an array of integers based on the specified conditions for odd and even numbers. The algorithm maintains the respective positions of odd and even values in the output array while sorting them as required.

This approach highlights how to manipulate arrays in Java effectively while solving a specific sorting issue in an engaging way. Happy coding!