Learn about collections in Java such as LinkedLists, HashSet, HashMap and more.

Java for Programmers

Collections is one of the most important topics for Java Programming. Without the proper knowledge of every collection type in Java, it becomes difficult for you to decide which option to pick in a particular scenario.

This course will give you a great understanding of all collection types available in the Collections Framework like lists, linked lists, sets, and hashmaps.

After completing this course, you will know how data can be modified within a collection, how to sort a collection, and how it can be made thread-safe. You will also cover the internal working of each Java collection so you can work with them more efficiently.

Java Collections

# Problem: Find duplicate element

 You are given an array in which all the elements are unique except one element. You need to find the duplicate element. 

For example, the array is {12, 34, 1, 56, 43, 34, 65}

The output should be 34 since it is the only duplicate element.

This problem should be done in $O(n)$ complexity, and the array is not sorted.

HashSet: Exercise