Java Coding Test Course, Arrays and Lists

1. Introduction

For programming beginners and aspiring developers, arrays and lists are fundamental data structures. Understanding these two data structures is crucial for achieving excellent performance in various coding test problems. In this article, we will solve an algorithm problem using arrays and lists in Java.

2. Problem Description

Problem: Write a method that removes duplicate elements from a given integer array and returns the remaining elements sorted. The result array should be sorted in ascending order, and duplicate values should be removed.

Problem Summary

• Input: Integer array
• Output: Array sorted in ascending order after removing duplicates

3. Example

Input: [3, 1, 2, 3, 4, 2, 1]
Output: [1, 2, 3, 4]

4. Approach

To solve this problem, we will follow these steps:

• Step 1: Remove duplicate elements from the input array.
• Step 2: Sort the remaining elements.
• Step 3: Return the final result.

5. Code Implementation

Now, let’s write the Java code based on the above approach.

        
import java.util.Arrays;
import java.util.HashSet;

public class RemoveDuplicatesAndSort {

    public static int[] removeDuplicatesAndSort(int[] arr) {
        // Use HashSet to remove duplicates
        HashSet set = new HashSet<>();
        for (int num : arr) {
            set.add(num);
        }

        // Convert unique elements to an array
        int[] uniqueArray = new int[set.size()];
        int index = 0;
        for (int num : set) {
            uniqueArray[index++] = num;
        }

        // Sort the array
        Arrays.sort(uniqueArray);
        return uniqueArray;
    }

    public static void main(String[] args) {
        int[] input = {3, 1, 2, 3, 4, 2, 1};
        int[] result = removeDuplicatesAndSort(input);
        System.out.println(Arrays.toString(result)); // [1, 2, 3, 4]
    }
}
        
    

Code Explanation

The above code defines a method called removeDuplicatesAndSort. This method removes duplicate elements from the input array and returns a sorted array.

• First, we use a HashSet to easily remove duplicate integers.
• Then we copy the contents of the HashSet into a new array.
• Finally, we use Arrays.sort to sort the array.

6. Complexity Analysis

The time complexity of this algorithm is as follows:

• Removing duplicates: O(n), where n is the size of the input array.
• Sorting: O(m log m), where m is the size of the array after duplicates have been removed.

Therefore, the overall time complexity is O(n + m log m).

7. Conclusion

In this tutorial, we implemented a duplicate removal and sorting algorithm using arrays and lists in Java. Through each step, we understood how basic data structures work and learned how to improve our skills. I hope you gain more experience by solving various algorithm problems in the future.

References

• Books on data structures and algorithms
• Java official documentation

8. Additional Practice Problems

Try the following problem as an additional exercise.

• Implement a method that removes duplicate values and returns a new array when given a sorted array.

Enhance your understanding of algorithms and improve your skills through coding practice!