Competitive Coding

What is algorithm?
Algorithm is well-define step by step procedure to solve the specific problem.

Why should you care ? why not just learn full stack dev.
    what is you job ? Solving Problems!
    problems:

• already solved : face detection, shorted route, ... (use external lib)
• specific to the company's needs:
• Facebook suggestions
  

Why do Big Companies ask algorithms in interviews? 

• Questions about language/technology 
• Algorithm ?
• Approaching newly seen problems 
• Discussing different approaches (brainstorming session)
• Articulation ideas, communication skills 
• Adaptability
• picking your brain :
  

Innovative product that uses algorithm?

• Google search being able to auto-correct and suggest
• google Maps directions : Dijkstra , A* , kd tree, range search
• Google translate and direction
• Self Driving cars
• Cleaning Robot detection the house map
• Space X making reusable spaceship that land back earth.
  

Correctness and Performance ?

• An algorithm is correct if it is gives you the desired outcome/output no mater the input you provide it with.
• Determining the correct of an Algorithm:
• easy: sum(a,b) return a + b
  
• hard : Kruskal's algorithm for MST
• Performance : How  fast  an algorithm executes depending on the input size
• Sometimes you can't have both -> NP-complete problems 
• NP-complete problems can't be solved in polynomial time
• They are solve in O(2^n), O()3^n),....time complexity.
• Sacrifice correctness for time: 
• O(2^n) > 100% accuracy
• O(3^n) > 87.5% accuracy
  
• O(n^2) > 79.2% accuracy

Example : Amazon courier delivering package in shortest time (Travelling Salesman Problem)

Introduction to Data Structure :

What is Data ?
Everything you see is a set of pixels(data):

What is Data Structures?
Only When arrange in a concise and structure way data becomes meaningfull.
In Computing data = bits(0's and 1's)
CPU(computer brain) makes bits meaningful 

Bits :

• numbers
• pixels
• decibels

Real-life example

• Arrays - Leader-board
• Matrices- Image processing
• Linked List - Playlistd
• Stack - Undo Redo functionality
• Queue - OS job scheduling
• Graph - Facebook friendship relations
• Tree - Hierarchy relations, HTML DOM Elements  
  

Complexity Analysis : 

 

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