Please read How to Think Recursively before reading this post. This post re-applies the steps mentioned in the previous post on a more challenging question. Question Return all possible ways we can generate a well-formed parenthesis? Examples: if n = 1 then we can only form () if n = 2 then we can form (()) and ()() if n = 3 then we can form ((())), (())(), ()(()), (()()), (), (), () Let’s try applying our 4 steps:...

These articles are about the gotchas I faced when trying to think recursively. The logic in principle should apply to most recursive problems. In this post, I will use the following question as a point of reference: Count how many ways you can climb a staircase. You can jump either one step at a time or two steps at a time. Example if there are 3 stair cases then you can either jump:...

I made some changes to the repo of our private pod. Pushed up my branch. Tests all ran. Then my colleague asked for some updates to my PR (pull request). I made changes and pushed it to GH. I wanted to merge the changes. But then CI was failing. So I ran CI again. It failed again. They say third time is the charm. So I ran it two more times....

My team was dealing with a large flow, where user can transition from multiple states or sometimes skip certain states. We didn’t have a centralized controller, every screen just had logic on where it should go next. This made it difficult for us to see all our logic at once. We asked around and was told state machines are a good fit for our situation. State machines are void of any UX....

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....

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....

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....

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....

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....

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....