Remove Duplicates from List in Java: Explanation & Practice

Problem summary

Write a program that removes duplicates from a list while maintaining original order.

Starter code

import java.util.*;

public class Main {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(1, 3, 2, 1, 4, 2, 3, 5, 4); // Test case 1
        
        // Remove duplicates, preserve order
        // Print space-separated
    }
}

Expected output and test cases

• Preserve first occurrence order

  1 3 2 4 5

• Different order

  5 4 3 2 1

• All same elements

  1

Hints

1. LinkedHashSet preserves insertion order
2. Or use ArrayList and check contains()
3. Convert back to list if needed

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• Practice Word Frequency Counter in Java
• Practice List Intersection in Java

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