First Unique Element in Java: Explanation & Practice

Problem summary

Use collections to find the first element in a list that appears exactly once.

Starter code

import java.util.*;

public class Main {
    public static void main(String[] args) {
        List<Integer> nums = Arrays.asList(1, 2, 1, 3, 2, 4, 3); // Test case 1
        
        // Find first unique element
        // Print: First unique: <element> OR No unique element
    }
}

Expected output and test cases

• 4 appears once

  First unique: 4

• First is unique

  First unique: 1

• All repeat

  No unique element

Hints

1. Count frequencies first with Map
2. Then iterate original list
3. Find first with count 1

Related Collections exercises

• Practice Priority Queue with Custom Order in Java
• Practice Two Sum with HashMap in Java
• Practice Merge K Sorted Lists in Java

Practice all Collections exercises · Run this idea in the Java compiler