Java

What we want to achieve Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack. Example 1:… Read More »How to ReImplement strStr() in Java

The challenge Given a non-empty array of integers, return the third maximum number in this array. If it does not exist, return the maximum number. The time complexity must… Read More »Third Maximum Number with Java

The challenge Given a string, find the first non-repeating character in it and return its index. If it doesn’t exist, return -1. Examples: s =… Read More »First Unique Character in a String using Java

What do you do when you create a new Maven Java project, and when you run it, you get the following error: Error:java: error: release… Read More »How to fix the Release Version 5 Not Supported error in IntelliJ

The challenge Given a 32-bit signed integer, reverse digits of an integer. Example 1: Input: 123 Output: 321 Example 2: Input: -123 Output: -321 Example… Read More »How to Reverse an Integer in Java

The challenge Write a function that reverses a string. The input string is given as an array of characters char[]. Do not allocate extra space for… Read More »Reverse a String in-place using Java

The challenge Given an array of integers, find if the array contains any duplicates. Your function should return true if any value appears at least… Read More »Check if a Java array Contains Duplicates

The challenge Students are asked to stand in non-decreasing order of heights for an annual photo. Return the minimum number of students that must move… Read More »The Array Height Checker Problem in Java

The challenge Given an array of integers A sorted in non-decreasing order, return an array of the squares of each number, also in sorted non-decreasing order. Example 1: Input:… Read More »Find the Squares of a Sorted Array in Java

The challenge Given an array A of non-negative integers, return an array consisting of all the even elements of A, followed by all the odd elements of A. You… Read More »Sorting a Java Array by Parity

Say you have an array of primitive integers and you want to remove all duplicates. You can find out how many non-duplicate integers are in… Read More »Remove Duplicates from Sorted Array in Java

The challenge Given an array arr, replace every element in that array with the greatest element among the elements to its right, and replace the last element with -1.… Read More »Replace Elements with Greatest Element on Right Side using Java

Introducing the problem Given an array A of integers, return true if and only if it is a valid mountain array. Recall that A is a mountain array if and… Read More »The Valid Mountain Array Problem using Java

The Challenge An encoded string S is given.  To find and write the decoded string to a tape, the encoded string is read one character at a time and the following… Read More »The Decoded String at Index using Java

In Java there are eight basic data types; which are: byte, short, int, long, float, double, boolean and char. It could realistically be said that… Read More »The Primary Data Types in Java

TLDR; Java has a few different ways of comparing variables and objects with one another. ==, equals(), compareTo() and compare(). Java provides various operators such… Read More »Comparing Objects in Java

As with many programming languages such as C, C++ and C# (known commonly as the C family), it is possible to “overload methods” (sometimes called… Read More »Overloading Operators in Java