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Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

A height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

Given a binary tree, determine if it is height-balanced.

A height-balanced binary tree is defined as: a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

Given two binary trees, write a function to check if they are the same or not.

Two binary trees are considered the same if they are structurally identical and the nodes have the same value.

Given a string containing just the characters (, ), {, }, [ and ], determine if the input string is valid.

An input string is valid if:

Open brackets must be closed by the same type of brackets.

Merge two sorted linked lists and return it as a new list. The new list should also be sorted.

Given a string s, find the longest palindromic substring in s.

Given an integer array numbers, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum.

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations:
get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.
put(key, value) - Set or insert the value for the given key in the cache. When the cache has reached its capacity, it should invalidate the least recently used item before inserting a new item.
The cache is initialized with a positive capacity.

Given an array of integers, return the indices of the two numbers whose sum is equal to a given target.
You may assume that each input would have exactly one solution, and you may not use the same element twice.

In this article, you'll learn how to convert a character to an ASCII code and vice versa in Java. The conversion from ASCII code to character and character to ASCII code is done using type casting.

In this article, you'll learn how to Base64 decode any Base64 encoded data back to binary data. Java 8's Base64 API provides implementations for Base64 encoding and decoding as described in RFC 4648.

In this article, you'll learn how to Base64 Encode a String in Java. Java 8 introduced a new class called Base64 which contains convenience functions to Base64 encode a sequence of bytes and also decode a Base64 encoded string.

Java URL Decoding example. Learn how to decode any URL encoded query string or form parameter in Java. Java Provides a URLDecoder class containing a method named decode(). It takes a URL encoded string and a character encoding as arguments and decodes the string using the supplied encoding.

Programmers often need to perform URL encoding on query strings or form parameters while calling a remote API or receiving data from a client. URL encoding makes the transmitted data more reliable and secure.

Java LinkedHashMap is a hash table and doubly linked List based implementation of Java's Map interface. It extends the HashMap class which is another very commonly used implementation of the Map interface.

A Queue is a First In First Out (FIFO) data structure. It models a queue in real-life. Yes, the one that you might have seen in front of a movie theater, a shopping mall, a metro, or a bus. Just like queues in real life, new elements in a Queue data structure are added at the back and removed from the front.

Java TreeMap is a Red-Black tree based implementation of Java's Map interface. The TreeMap class is part of Java's collection framework. It implements the NavigableMap interface, which in turn extends the SortedMap interface.

Java HashSet class is a member of Java collections framework. It implements the Set interface. HashSets are used to store a collection of unique elements.

ArrayList in Java is used to store dynamically sized collection of elements. Contrary to Arrays that are fixed in size, an ArrayList grows its size automatically when new elements are added to it. ArrayList is part of Java's collection framework and implements Java's List interface.

Java HashMap is a hash table based implementation of Java's Map interface. A Map, as you might know, is a collection of key-value pairs. It maps keys to values.

Learn how to create and write to an excel file or modify an existing excel file using Apache POI library.