» CS 145 Lecture 30 – Higher Dimensions

CS 145 Lecture 30 – Higher Dimensions

November 13, 2015 by Chris Johnson. Filed under cs145, fall 2015, lectures.

Agenda

what ?s
arraylistercise
arrays to higher dimensions

TODO

Read sections 7.3 through 7.5 in the book. Share 2-3 questions or observations on a 1/4 sheet.
Start homework 6. Due before November 30.
The challenge for the second and final mercy fortnight will involve finishing homework 7 on objects before December 7. The regular due date will be before December 14. Homework 7 will be released before break and achieving it will give you the opportunity to resubmit homeworks 4, 5, and 6 before the final exam.

Note

Last time we looked at managing “growable” arrays with the ArrayList class:

  1: /usr/lib/ruby/2.7.0/rubygems/dependency.rb:311:in `to_specs': Could not find 'coderay' (>= 0) among 56 total gem(s) (Gem::MissingSpecError)
Checked in 'GEM_PATH=/.gem/ruby/2.7.0:/var/lib/gems/2.7.0:/usr/lib/ruby/gems/2.7.0:/usr/share/rubygems-integration/2.7.0:/usr/share/rubygems-integration/all:/usr/lib/x86_64-linux-gnu/rubygems-integration/2.7.0:/home/johnch/.gems', execute `gem env` for more information
	from /usr/lib/ruby/2.7.0/rubygems/dependency.rb:323:in `to_spec'
	from /usr/lib/ruby/2.7.0/rubygems/core_ext/kernel_gem.rb:62:in `gem'
	from ./coderay:24:in `'
ArrayList<Person> people = new ArrayList<Person>();
  2: Random g = new Random();...
  3: people.add(g.nextPerson());...
  4: people.add(g.nextPerson());...
  5: people.add(g.nextPerson());...
  6: people.add(g.nextPerson());...
  7: people.add(g.nextPerson());...
  8: System.out.println(people.size());...
  9: System.out.println(people.get(1).getName());...
 10: people.get(4).jump(3);...
 11: people.get(0).highFive(people.get(3));...
 12: people.add(people.get(2));...
 13: people.remove(2);...
 14: ...
 15: for (int i = 1; i < people.size(); i += 2) {...
 16:   people.get(i).sit();...
 17: }...
 18: System.out.println(sum);...
 19: ...
 20: int sum = 0;...
 21: for (int i = 0; i < people.size(); ++i) {...
 22:   sum += people.get(i).getCourses(Semester.FALL, 2015).size();...
 23: }...
 24: System.out.println(sum);...
 25: ...
 26: Person winner = people.get(0);...
 27: for (int i = 1; i < people.size(); ++i) {...
 28:   if (people.get(i).getDateOfBirth().isBefore(winner.getDateOfBirth())) {...
 29:     winner = people.get(i);...
 30:   }...
 31: }...
 32: System.out.println(winner.getName());...
 33: ...
 34: Person tmp = people.get(2);...
 35: people.set(2, people.get(1));...
 36: people.set(1, tmp);...
 37: ...
 38: for (int i = 0; i < people.size(); ++i) {...
 39:   for (int j = 0; j < people.size(); ++j) {...
 40:     if (i != j) {...
 41:       people.get(i).shakeHands(people.get(j));...
 42:     }...
 43:   }...
 44: }...
 45: ...
 46: people.clear();[/precode]...

...

Now, we missed a blackbox the other day that grows our idea of arrays into higher dimensions. Let’s have look:

Blackbox 20

To solve this we need to make arrays in higher dimensions. We saw the general pattern for making an array:

type[] id = new type[n];

The type can be anything, even another array. Suppose we want an array of int arrays? Then we substitute int[] in for type:

int[][] id = new int[outerN][innerN];

We’ll look at two-dimensional arrays through the lens of the birthday problem and generating all prefixes of an array.

Code

Prefices.java

/usr/lib/ruby/2.7.0/rubygems/dependency.rb:311:in `to_specs': Could not find 'coderay' (>= 0) among 56 total gem(s) (Gem::MissingSpecError)
Checked in 'GEM_PATH=/.gem/ruby/2.7.0:/var/lib/gems/2.7.0:/usr/lib/ruby/gems/2.7.0:/usr/share/rubygems-integration/2.7.0:/usr/share/rubygems-integration/all:/usr/lib/x86_64-linux-gnu/rubygems-integration/2.7.0:/home/johnch/.gems', execute `gem env` for more information
	from /usr/lib/ruby/2.7.0/rubygems/dependency.rb:323:in `to_spec'
	from /usr/lib/ruby/2.7.0/rubygems/core_ext/kernel_gem.rb:62:in `gem'
	from ./coderay:24:in `'

Bepeats.java

/usr/lib/ruby/2.7.0/rubygems/dependency.rb:311:in `to_specs': Could not find 'coderay' (>= 0) among 56 total gem(s) (Gem::MissingSpecError)
Checked in 'GEM_PATH=/.gem/ruby/2.7.0:/var/lib/gems/2.7.0:/usr/lib/ruby/gems/2.7.0:/usr/share/rubygems-integration/2.7.0:/usr/share/rubygems-integration/all:/usr/lib/x86_64-linux-gnu/rubygems-integration/2.7.0:/home/johnch/.gems', execute `gem env` for more information
	from /usr/lib/ruby/2.7.0/rubygems/dependency.rb:323:in `to_spec'
	from /usr/lib/ruby/2.7.0/rubygems/core_ext/kernel_gem.rb:62:in `gem'
	from ./coderay:24:in `'

Haiku

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