Arrays

Today we’re solving https://leetcode.com/problems/asteroid-collision/ Imagine if we had the following: 1 5 3 8 6 -> -> <- <- -> Each number represents the size of an asteroid. Each asteroid is either going left or right. Bigger asteroids destroy smaller asteroids. Asteroids with same size both get destroyed. If two asteroids are going in the same direction, they don’t hit each other, because all are going in the same speed. The challenge is to return: which asteroids will remain at the end? ...

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.e. ascending }) If you see $0 < $1 then left side is smaller than the next item. i.e. it’s ascending. ...

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. I guess the “middle” are those two indices.‌‌ ‌But then you have to pick one. For this reason it’s often better to think of it as a pivot because it’s really the 2nd index. The 2nd index isn’t the middle index of a 4 element array. ...