☕ Elon Musk's School
Elon Musk's school is going mainstream with remote learning. Simulate evolution in Rust and TailwindCSS's solution to large development CSS files. Plus a solution to yesterday's interview question.
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source  XKCD
Industry News
Josh Dahn (cofounder with Elon Musk for Ad Astra) raises a fundraising round for Synthesis
Ad Astra (now known as AstraNova) is a school created by Elon Musk and Josh Dahn that focuses on teaching children critical thinking, independent thought and problem solving skills.
All of Elon Musk’s children attend Ad Astra, and the school has only been open to children of SpaceX employees (the school is located on the SpaceX campus).
Now, Josh Dahn wants to bring this educational experience to everyone.
Josh Dahn has teamed up with Chrisman Frank, an early employee at ClassDojo, to create an online school that puts children ages 7  14 through a course that teaches leadership, teamwork, independent thought, critical thinking and other useful skills.
The company has grown incredibly fast, with 50% monthly compounded growth since the start of November. They’re now doing over a $1 million dollars in annual run rate.
More than 85% of the students stay in the program after 90 days.
The school is now raising a round of fundraising. Current investors include Alexis Ohanian (cofounder of Reddit), Sam Teller (Elon’s former Chief of Staff), Austin Rief (founder of Morning Brew) and many others.
You can view the company here.
Tech Snippets

The Next Generation of TailwindCSS: JustInTime
 TailwindCSS is an amazing CSS framework that allows you to write CSS using Utility classes placed directly in your HTML. It’s been exploding in popularity over the past 2 years.
 One of the hardest constraints is the size of the generated CSS file in development, which can reach 10mb or more.
 Tailwind is fixing these issues with a justintime compiler for TailwindCSS that compiles your CSS ondemand as you author your files, instead of generating the entire stylesheet up front.
 Simulating Evolution in Rust  an awesome series on genetic algorithms and neural networks. Implemented in Rust, but no background knowledge is required.
Interview Question
You’re given an infinite complete binary tree.
Every level of the tree is filled with values from 1 to infinity.
However, the ordering of the nodes has been flipped for even numbered rows, where they go from largest to smallest.
Given the label of a node in this tree, return the labels in the path from the root of the tree to that row.
Example
Input: 14
Output: [1, 3, 4, 14]
Can you solve this in O(log n) time?
We’ll send a detailed solution in our next email, so make sure you move our emails to primary, so you don’t miss them!
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Previous Solution
As a refresher, here’s the last question
Given the root of a Binary Tree, return the sum of the values in the trees’ deepest leaves.
Example
Answer = 15 since 7 + 8 = 15
Solution
We can solve this question with a Breadth First Search or a Depth First Search.
We’ll do a DFS here with a preorder traversal.
We’ll first create a list with two elements.
The first element keeps track of the deepest depth we’ve come across in our traversal.
The second element keeps track of the sum of the leaves at that depth.
Now, we can implement our preorder traversal.
In our traversal, we add an extra parameter to keep track of the depth of the current node.
When we process the node, we first check if the node is a leaf.
If so, then we check if the depth of it is greater than the deepest depth we’ve come across (in our list).
If so, then we set the deepest depth to the current depth and we set the leaf sum to our current node’s value.
Otherwise, we check if the depth of the current node is equal to the deepest depth we’ve come across.
If this is the case, then we add the current node’s value to to our leaf sum.
If the node isn’t a leaf, then we just continue traversing through it’s children.
After the traversal, we can return the leaf sum of the deepest nodes.