self-contained rv

What Resources Does Apple Provide for teaching iOS to students?

Note: This post has got a bit longer than what I originally intended. You might want to skip to the very end to see the verdict and table first and then read again. I’ve started an iOS training course in my local community. At the beginning I thought it would be easy for me to just start training people with whatever I know. Later I decided to look at some available resources....

September 21, 2022 · 9 min

Longest Increasing Subsequence Length

What’s a subsequence? Any selection of items from the original array. The selection must respect the order. Meaning for [1,2,3,4,5] only two of the four below are subsequences: [1,2,3,4,5] ✅ [1,4,3,2,5] ❌ order not respected [1,2,5] ✅ [5,1] ❌ order not respected What’s the difference between a subsequence and a subarray? Subarray, is just like subsequence, that is order must be respected. Additionally the sub-array has to be made of continuous elements....

August 25, 2022 · 3 min

Which Way Am I Sorting?

I always got confused as to what’s the end result my sort. I wasn’t sure if it would end up being ascending or descending. The ultimate trick is to not think of up vs down. Instead think of increasing/decreasing from left to right. We perceive arrays as horizontal beings. Hence left and right make more sense vs up and down let nums = [1,4,2,3] let sorted_nums = arr.sorted(by: { $0 < $1 // left is smaller [1,2,3,4] i....

August 3, 2022 · 1 min

Recover Binary Tree

Question: You have a binary tree. But only two of its elements have been swapped. This makes it a faulty binary tree. The challenge is to swap those two elements. And fix the tree. Solution I knew I had to traverse it. But then what? With a little help from reading online, I realized I should traverse it, and store the values into an array. Then you just loop the array and find the bad indexes....

June 27, 2022 · 4 min

How to Calculate the Middle Index?

A good number of interview questions require you to constantly split an array/string in half. This is relatively easy to achieve when the array count is odd. However when the count is even, it’s not as easy. let a = [1,3,8,10,22] // middle index is 2 let b = [1,3,8,10] // middle index is 1.5 which is non-existent. So what now? Most important thing to note is: There’s no such thing as “middle index” when the count is even, I mean there’s two middles in that case....

June 19, 2022 · 3 min

Unicode Security

This post is the result of some post-discussion on my Swift Strings for iOS interviewing post. Given that characters look like one another or that are invisible codepoints I thought there might be some room for abuse. Luckily Unicode has great documentation security. At the high level there are two types of security issues: Visual Security Issues Suppose that the user gets an email notification about an apparent problem in their Citibank account....

June 17, 2022 · 5 min

Compress String

Question A simple compression algorithm would be to replace repeating characters with their count. Example aaa --> a3 aaabb --> a3b2 aaabbaa --> a3b2a2 Want to stand out? Ask if there’s a difference between a & A and if you need to add uppercase & lowercase together or need to separate them. In my implementation I assumed they’re different. Code // start counting, then upon seeing a diff, write the count....

June 15, 2022 · 1 min

Check if Two Strings Are One Edit Away

Question You can edit a string in three different ways: insert, remove or replace a character. Write a function to see if two strings are one or zero edits away. Example like, like --> true (zero edits) like, likes --> true (one edit: remove/insert) like, life --> true (one edit, replace) like, lik --> true (one edit: remove/insert) like, pine --> false (two edits) like, lion --> false (two edits) Strategy For most questions that require you to return true or false, you can reduce the scope of the question by removing noise....

June 15, 2022 · 2 min

Swift Strings for iOS interviewing

This is bit of fast paced intro into Swift Strings. ASCII, Unicode and the challenges they introduce. ASCII Ages ago, only characters that existed were just a to z, A to Z, and bunch of other English characters. This was problematic. You were limited to only 7 bits i.e. only 2 ^ 7 - 1 = 127 characters. Also non-English characters where not part of ASCII. Literally the name says ‘American Standard Code for Information Interchange’....

June 12, 2022 · 6 min

How to Prepare Yourself as a Podcast Guest?

The first time I listened to an iOS podcast was yrs ago. I was struggling to grasp basic iOS concepts and podcasts weren’t really covering basic technical material. It just didn’t seem like the right way of learning about things. Two weeks ago I got invited to Side Project Spotlight Podcast. I was thrilled but also clueless. Had to do some googling, listen to a few episodes and purchase some equipment....

May 12, 2022 · 6 min