Get Distinct Shapes

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Roblox Interview Problem

BST insertion

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Find corresponding Node of a second tree, given the node of a tree

See the Pen Corresponding DOM Node in 2nd DOM Tree by Dhiviya Dhanasekar (@dhiviyadhanasekar) on CodePen.

Apple Phone Interview Question

Someone recently asked me what's the point of such questions where you get something from one tree and find something based on it in a second tree. Such kind of algorithms are useful for libraries like React. React is a UI development library that has optimized rendering for the browser. 

The browser renders HTML in the form of DOM (Document Object Model) tree. Any update to the DOM is cascaded down this tree (involves tree processing complexity) and then the browser re-paints the changes. And these operations on the DOM tree are all pretty expensive.

What React does is to create a copy of the HTML DOM - this copy DOM tree is called the Shadow DOM. Any update you make to the DOM is first made on the Shadow DOM and then all the updates are batched together and sent to the actual HTML DOM. As a result, the number of times the browser re-paints the DOM is highly reduced. Thus using React provides you with faster/optimized renderings. 

In order for React to do what it does with it's own shadow tree and the HTML DOM Tree, it needs to do things with one tree and transfer it to the other tree. 

Maximum Depth of Binary Tree

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Pangram

Subdomain visit count

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Intersecting clickstream data

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Most Frequent Subtree Sum

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Two Sum

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Box Stacking - Dynamic Programming

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Length of the longest substring

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String to Leet

See the Pen String to Leet by Dhiviya Dhanasekar (@dhiviyadhanasekar) on CodePen.

Lessons Learnt:

mapper = {'a': 0};

if(mapper['a']) ---> is false

0 || undefined ---> is undefined

undefined || 0 ---> is 0

Create a line on a graph given 2 coordinates that define the line

See the Pen Graph Line Plot by Dhiviya Dhanasekar (@dhiviyadhanasekar) on CodePen.

Binary Heap properties

 A Binary Heap is a Binary Tree with following properties.

1) It’s a complete tree (All levels are completely filled except possibly the last level and the last level has all keys as left as possible). This property of Binary Heap makes them suitable to be stored in an array.

2) A Binary Heap is either Min Heap or Max Heap. In a Min Binary Heap, the key at root must be minimum among all keys present in Binary Heap. The same property must be recursively true for all nodes in Binary Tree. Max Binary Heap is similar to MinHeap.

• Arr[(i-1)/2]	Returns the parent node
  Arr[(2*i)+1]	Returns the left child node
  Arr[(2*i)+2]	Returns the right child node

Arr[(n/2) .... (n-1)] => will contain the leaf nodes, if n is the length of the array or total number of nodes.

The traversal method use to achieve Array representation is Level Order


Source: geeks for geeks

Binary Tree - DFS Preorder (Stacks)

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Binary Tree - DFS PostOrder (Recursion)

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Binary Tree - DFS PreOrder (Recursive)

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Binary Tree - DFS Inorder Traversal (Recursion)

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Tree BFS in JS (Queue/Array)

Tree properties

1. The maximum number of nodes at level ‘l’ of a binary tree is 2^l
2. The Maximum number of nodes in a binary tree of height ‘h’ is 2^h – 1, Height of a tree with a single node is considered as 1.

BFS Complexity
Time Complexity - O(n)
Space Complexity - O(n)

Notes: BFS slower than DFS

From geeksforgeeks: 

Extra space required for Level order traversal is likely to be more when tree is more balanced and extra space for Depth First Traversal is likely to be more when tree is less balanced.

How to Pick One?

1. Extra Space can be one factor (Explained above)
2. Depth First Traversals are typically recursive and recursive code requires function call overheads.
3. The most important points is, BFS starts visiting nodes from root while DFS starts visiting nodes from leaves. So if our problem is to search something that is more likely to closer to root, we would prefer BFS. And if the target node is close to a leaf, we would prefer DFS.

Exercise:
Which traversal should be used to print leaves of Binary Tree and why? DFS
Which traversal should be used to print nodes at k’th level where k is much less than total number of levels? BFS

See the Pen Tree BFS in JS (Recursive & Non-recursive Queue versions) by Dhiviya Dhanasekar (@dhiviyadhanasekar) on CodePen.

LinkedList functions in JS

See the Pen JS LinkedList by Dhiviya Dhanasekar (@dhiviyadhanasekar) on CodePen.