Computer Science: The Good Parts @jeffcohen Jeffrey Cohen csthegoodparts.com

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http://imgs.xkcd.com/comics/the_general_problem.png

The Good Parts Data Structures Algorithms Complexity Classification Computational Thinking Culture of Innovation

Data Structures and Algorithms A data structure is a way to organize data. Different data structures exist for a reason.

Data Structures and Algorithms A data structure is a way to organize data. Different data structures exist for a reason. List Array Hash Tree Graph

Data Structures and Algorithms A data structure is a way to organize data. Different data structures exist for a reason. List Array Hash Tree Graph

Data Structures and Algorithms A data structure is a way to organize data. Different data structures exist for a reason. List Array Hash Tree Graph a

Data Structures and Algorithms A data structure is a way to organize data. Different data structures exist for a reason. List Array Hash Tree Graph a

Data Structures and Algorithms A data structure is a way to organize data. Different data structures exist for a reason. List Array Hash Tree Graph a a[0] a[1] a[2] a[3]

Data Structures and Algorithms A data structure is a way to organize data. Different data structures exist for a reason. List Array Hash Tree Graph :name => “Jeff” :id => 2 …. :email => “j@..” params[:id]

Data Structures and Algorithms List Array Hash Tree Graph Jeff Alice Bob Amy Dave

Data Structures and Algorithms List Array Hash Tree Graph Jeff Alice Bob Amy Dave

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Data Structures and Algorithms Select the data structure that resembles the real-life problem that you’re trying to solve.

Data Structures and Algorithms An algorithm computes a result by operating upon a data structure.

Data Structures and Algorithms An algorithm computes a result by operating upon a data structure. Charles Babbage Ada Lovelace

Data Structures and Algorithms

Margaret Hamilton Source code of the Apollo Guidance Computer

An algorithm computes a result by operating upon a data structure. Data Structures and Algorithms The complexity of an algorithm depends upon the data structure it is forced to work with.

Big “O” Notation O( ) O(n) O(log n) O(n^2)

Big “O” Notation def search(name_to_find) @people.each do |person| if person.name == name_to_find return person end end return nil end

O(n) def @people end 0 100 200 300

Big “O” Notation def search(name_to_find, from = 0, to = nil) to ||= @people.count - 1 mid = (from + to) / 2 if name_to_find < @people[mid].name search(@people, value, from, mid-1) elsif name_to_find > @people[mid].name search(@people, value, mid+1, to) else @people[mid] end end

O(log n) def to mid search(@people, value, from, mid search(@people, value, mid @people end 0 100 200 300

Big “O” Notation def calculate_total(customer) total = 0 customer.orders.each do |order| order.line_items.each do |item| total += item.price end end total end

O(n2) def total customer order total total end 0 100 200 300

http://blog.atom.io/

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Alan Turing

Computational Thinking Computer science is not computer programming. It’s the pursuit of understanding how humans think and solve problems.

Stand on Shoulders

Applied Science! ★ Watch out for loops ★ Watch out for nested loops ★ Learn every kind of Ruby data structure ★ Solve a tiny problem from first principles, without a database nor any gems: just the Ruby standard library. ★ Try to classify the “complexity” of your code. ★ Read the code inside every gem in your Gemfile. ★ Learn how to use the Benchmark class ★ Join the tradition of accomplishing something meaningful

Computer Science: The Good Parts @jeffcohen Jeffrey Cohen csthegoodparts.com