teaching machines

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 `
'

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