Squares of a Sorted Array - Java Solution

🎓 Top 15 Udemy Courses (80-90% Discount): My Udemy Courses - Ramesh Fadatare — All my Udemy courses are real-time and project oriented courses.

▶️ Subscribe to My YouTube Channel (178K+ subscribers): Java Guides on YouTube

▶️ For AI, ChatGPT, Web, Tech, and Generative AI, subscribe to another channel: Ramesh Fadatare on YouTube

1. Introduction

In this blog post, we will explore a simple yet interesting array processing problem: squaring each number in a sorted array and then returning a new array that is also sorted. This problem is a good test of understanding array manipulation and sorting in Java.

Problem

Given an array of numbers sorted in increasing order, the task is to return a new array containing squares of all the numbers of the input array, sorted in increasing order.

Example 1:

Input: a[] = [-5, -2, -1, 0, 4, 6]

Output: [0, 1, 4, 16, 25, 36]

Example 2:

Input: nums = [-5, -4, -3, -2, -1]

Output: [1, 4, 9, 16, 25]

Example 3:

Input: nums = [1, 2, 3, 4, 5]

Output: [1, 4, 9, 16, 25]

2. Solution Steps

1. Initialize two pointers at the start and end of the array.

2. Create a new array for the result.

3. Compare the absolute values of elements pointed by the two pointers.

4. Square the larger absolute value and put it in the result array.

5. Move the pointers accordingly and repeat until the entire array is processed.

6. Return the result array.

3. Code Program

public class Solution {

    // Main method for testing
    public static void main(String[] args) {
        int[] a1 = {-5, -2, -1, 0, 4, 6};
        int[] a2 = {-5, -4, -3, -2, -1};
        int[] a3 = {1, 2, 3, 4, 5};

        System.out.println("Squared and sorted array: " + Arrays.toString(makeSquares(a1)));
        System.out.println("Squared and sorted array: " + Arrays.toString(makeSquares(a2)));
        System.out.println("Squared and sorted array: " + Arrays.toString(makeSquares(a3)));
    }

    // Method to create a new sorted array of squares
    public static int[] makeSquares(int[] nums) {
        int n = nums.length;
        int[] squares = new int[n];
        int highestSquareIdx = n - 1;
        int left = 0, right = n - 1;

        while (left <= right) {
            int leftSquare = nums[left] * nums[left];
            int rightSquare = nums[right] * nums[right];

            if (leftSquare > rightSquare) {
                squares[highestSquareIdx--] = leftSquare;
                left++;
            } else {
                squares[highestSquareIdx--] = rightSquare;
                right--;
            }
        }

        return squares;
    }
}

Output:

Squared and sorted array: [0, 1, 4, 16, 25, 36]
Squared and sorted array: [1, 4, 9, 16, 25]
Squared and sorted array: [1, 4, 9, 16, 25]

Explanation:

The makeSquares method processes the input array from both ends using two pointers. It squares the numbers and stores them in the result array from the highest index to the lowest, ensuring the result is sorted. 

For example, with the input array [-5, -2, -1, 0, 4, 6], it squares the numbers and arranges them as [0, 1, 4, 16, 25, 36], which is the sorted array of squares.

My Top and Bestseller Udemy Courses. The sale is going on with a 70 - 80% discount. The discount coupon has been added to each course below:

Build REST APIs with Spring Boot 4, Spring Security 7, and JWT

🆕 High-Demand 80–90% OFF

[NEW] Learn Apache Maven with IntelliJ IDEA and Java 25

🆕 High-Demand 80–90% OFF

ChatGPT + Generative AI + Prompt Engineering for Beginners

🚀 Trending Now 80–90% OFF

Spring 7 and Spring Boot 4 for Beginners (Includes 8 Projects)

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Building Real-Time REST APIs with Spring Boot - Blog App

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Building Microservices with Spring Boot and Spring Cloud

🌟 Top Rated 80–90% OFF
Available in Udemy for Business

Java Full-Stack Developer Course with Spring Boot and React JS

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Build 5 Spring Boot Projects with Java: Line-by-Line Coding

🌟 Top Rated 80–90% OFF

Testing Spring Boot Application with JUnit and Mockito

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Spring Boot Thymeleaf Real-Time Web Application - Blog App

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Master Spring Data JPA with Hibernate

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Spring Boot + Apache Kafka Course - The Practical Guide

🎓 Student Favorite 80–90% OFF
Available in Udemy for Business

Java Testing: Mastering JUnit 5 Framework

🆕 New 80–90% OFF

Reactive Programming in Java: Spring WebFlux and Testing

🌟 Top Rated 80–90% OFF

Spring Boot + RabbitMQ Course - The Practical Guide

🌟 Top Rated 80–90% OFF
Available in Udemy for Business

Functional Programming in Java (Includes Java Collections)

🎓 Student Favorite 80–90% OFF

ChatGPT for Java Developers: Boost Your Productivity with AI

🚀 Trending Now 80–90% OFF