Computer Science: The Good Parts (2016)

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Computer Science: The Good Parts @jeffcohen

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The Good Parts Data Structures Algorithms Computational Thinking Culture Complexity

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

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Data Structures Algorithms List Array Hash Tree Graph 2 5 1 9 v

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Data Structures Algorithms List Array Hash Tree Graph 2 5 1 9 a a[0] a[1] a[2] a[3]

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Data Structures Algorithms List Array Hash Tree Graph h purple color baseball sport cookies fruit

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Data Structures Algorithms List Array Hash Tree Graph

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Data Structures Algorithms List Array Hash Tree Graph h purple color baseball sport cookies fruit

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

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

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Data Structures Algorithms • Who's status updates would I like to see? • What should I buy? • What advertisement would inﬂuence my behavior the most right now? • I'm bored. How do I get to the pool? • Our website crashed. How do we get our airplane schedule back to normal?

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Dijkstra's Algorithm Traveling Salesman Problem Data Structures Algorithms Graph Theory

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

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Culture: Knowing vs. Understanding

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

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

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Data Structures Algorithms

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Margaret Hamilton Source code of the Apollo Guidance Computer

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

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O( ) O(n) O(log n) O(n^2) Complexity: "Big O" Notation

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def search(people, name_to_find) for person in people if person.name == name_to_find return person end end return nil end Complexity: "Big O" Notation

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0 100 200 300 O(n) Complexity: "Big O" Notation

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def search(people, 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 Complexity: "Big O" Notation

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O(n) 0 100 200 300 O(n) O(log n) Complexity: "Big O" Notation

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def calculate_total(customer) total = 0 for order in customer.orders do for item in order.line_items do total += item.price end end total end Complexity: "Big O" Notation

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O(n2) def calculate_total(customer) total = 0 customer.orders.each do |order| order.line_items.each do |item| total += item.price end end total end 0 100 200 300

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The Test Kitchen

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http://blog.atom.io/

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Alan Turing

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

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• Break problems into small pieces. • Focus on one thing at a time. • Follow the recipe of a proof. • Make the invisible visible. • Do the simplest thing that can possibly work. • Describe your problem out loud (rubber ducky!) • There's no problem that another level of indirection can't solve. :-)  Computational Thinking

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Grace Hopper

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You don't manage people; you manage things.    You lead people.

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Humans are allergic to change. They love to say, "We've always done it this way." I try to ﬁght that.    That's why I have a clock on my wall that runs counter- clockwise.

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A ship in port is safe; but that is not what ships are built for. Sail out to sea and do new things.

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Stand on Shoulders

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Applied Science! • Watch out for nested loops. • Know how to use different data structures. • Solve a problem from ﬁrst principles. • Try to classify method “complexity” (Big O). • Read the source of code you use. • Learn how to benchmark your code. • Join the tradition of doing something meaningful!     

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