How to ReImplement strStr() in 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:
Input: …Read Article →
Technical Articles
In-depth guides, insights, and best practices for modern software engineering
Third Maximum Number with 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 …
Read Article →How to Quickly Hide all Icons on a Mac’s Desktop
Why the need to hide icons?
Perhaps you have a screen-share session coming up and you want a nice clean desktop to show everyone. Also, nobody will …
First Unique Character in a String using 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 Article →
How to fix the Release Version 5 Not Supported error in IntelliJ
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 version 5 not …
Facebook’s custom IPv6 range
I noticed an interesting thing with a certain visitor after posting a blog post to Facebook.
The IP address that the Facebook crawler uses to visit …
Read Article →How to Reverse an Integer in Java
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 …Read Article →
Reverse a String in-place using 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 Article →Check if a Java array Contains Duplicates
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 Article →Find All Numbers Disappeared in an Array using Python
The challenge
Given an array of integers where 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.
Find all the …
Read Article →The Array Height Checker Problem in Java
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 Article →Find the Squares of a Sorted Array 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 …
Sorting a Java Array by Parity
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 …
Remove Duplicates from Sorted Array in Java
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 the array …
Read Article →Replace Elements with Greatest Element on Right Side using 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 …
The Valid Mountain Array Problem 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 …
Read Article →HashMaps (aka: Dictionaries) in Python
Introduction
Java has a built-in called HashMap. It allows you to store and very quickly retrieve key value pairs.
In Python, this is called a …
Read Article →Find Numbers with Even Number of Digits using Java
The challenge
Given an array nums of integers, return how many of them contain an even number of digits.
Example 1:
Input: nums = [12,345,2,6,7896] …Read Article →
The Relational Database Model
Relational databases first made an appearance in the mid-1970s, between the years 1974 and 1977 with the creation of Ingres and System R which led to …
Read Article →How to use a Java HashSet by example
What is a HashSet
A HashSet is an unordered collection containing unique elements. It has the standard collection operations Add, Remove, Contains, …
Get The Shortest Path in Binary Matrix using Python
The challenge
In an N by N square grid, each cell is either empty (0) or blocked (1).
A clear path from top-left to bottom-right has length k if and …
Palindrome Partitioning in Python
The problem
Given a string s, partition s such that every substring of the partition is a palindrome.
Return all possible palindrome partitioning of s …
Read Article →Faster alternative to MySQL Delete Table Contents / Truncate
From time to time you might have some rather big tables that you want to delete all the data quickly and start afresh.
You have a few options at this …
Read Article →Best Time to Buy and Sell Stock with Python
The problem
Say you have an array prices for which the ith element is the price of a given stock on day i.
Design an algorithm to find the maximum …
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